If you are not using the OneSignal WordPress plugin see our Troubleshooting Web Push Guide. Otherwise, if you followed our WordPress Setup Video chances are you are almost done with setup!

Common setup issues

OneSignal Dashboard Setup

1. Incorrect Configuration

Make sure you selected "WordPress". The other setup options will not work with the plugin.

2. Check your Site URL

Make sure your site url is correct.

www and non-www are different. Set version based on your site url in WordPress General Settings.
Ignore Subdirectories having a subdirectory like /blog does not affect this and can be ignored for setup purposes.

OneSignal WordPress Plugin Setup

1. Do Not Use the OneSignal Init code

The OneSignal WordPress plugin automatically adds the code to your site needed for OneSignal to work. You should not add any initialization code to your WordPress site.

If you added the following code to your site, simply remove it. Here is what it looks like:

<script src="https://cdn.onesignal.com/sdks/OneSignalSDK.js" async=""></script>
<script>
  window.OneSignal = window.OneSignal || [];
  OneSignal.push(function() {
    OneSignal.init({
      appId: "YOUR_ONESIGNAL_APP_ID",
    });
  });
</script>

Then, make sure you selected the WordPress Configuration in your onesignal.com dashboard.

2. Incorrect App Id

In the onesignal.com dashboard > Your App > Settings > Keys & IDs
Make sure your OneSignal App ID and REST API Key match inside the OneSignal WordPress plugin. Press Save at the bottom of the plugin if you change this.

3. WordPress Plugin Disabled

At the bottom of the OneSignal WordPress Plugin, make sure you did not disable the plugin. If you see this disabled, no users can subscribe. Press Save at the bottom of the plugin if you change this.

This is for advanced customizations. See WordPress Customizations for details.

4. Wrong Browser, Viewing Mode, or Browser Version

Make sure you are testing with Chrome, Firefox or Safari (macOS). Brave does not support Push Notifications. Do not use private browser mode, incognito mode, guest browser mode or Firefox's ESR versions. Notifications do not work in these cases.

Debugging Your Plugin Setup

OneSignal prints helpful error messages on your browser's Developer Tools Console when viewing your site with the OneSignal code active. To open the Developer Tools Console:

Go to your website with the OneSignal Plugin Active
Right click on the page and select Inspect
Select the Console tab

Usually we print the direct cause of the error on the console and a link to the solution.

403 & 404 Service Worker Errors

After you try subscribing to your site, if you see a 403 or 404 error like this:

In you see 403 or 404 Service Worker Errors, that means something is blocking the following files from being publicly accessible:

https://yoursite.com/wp-content/plugins/onesignal-free-web-push-notifications/sdk_files/OneSignalSDKWorker.js.php
https://yoursite.com/wp-content/plugins/onesignal-free-web-push-notifications/sdk_files/OneSignalSDKWorker.js

Cannot convert undefined or null to object

In the Code the OneSignal plugin adds to your site, you should see this:

oneSignal_options['path'] = "https://yoursite.com/wp-content/plugins/onesignal-free-web-push-notifications/sdk_files/";

If this url (example yoursite.com ) does not match your site, then in the wp-config.php file add:

define("ONESIGNAL_PLUGIN_URL", "https://yoursite.com/wp-content/plugins/onesignal-free-web-push-notifications/");

Where yoursite.com is your actual site url.

Common Wordpress issues and fixes:

You selected the Typical Setup in the OneSignal Dashboard. Please make sure you selected the WordPress Setup in the onesignal.com dashboard. This is the most common mistake as shown above for Incorrect WordPress OneSignal Configuration
If you are using a CDN or Cache Plugin see WordPress CDN & Cache Plugin Support below.
If you are using a Security plugin, see these common security plugin issues.
Check that your .htaccess file sitting in the wp-content folder is not blocking php files.
Make sure not to be minifying CSS
Contact your hosting provider and ask them to whitelist these files. Here's a support ticket you can use:

Hi!
My site runs the OneSignal web push notifications plugin and we are having some issues with serving certain files. 
The OneSignal plugin team would like to request an exception on URLs including the string "onesignal-free-web-push-notifications".
Could you please add the above string to the exception list?
Thanks!

WordPress CDN & Cache Plugin Support

Using caching plugins with CDN support can cause files required to be served from your domain to be served from the CDN instead. Here's how to use the appropriate settings:

Autoptimize

In Excluded scripts section, exclude the OneSignal Script:

wp-content/plugins/onesignal-free-web-push-notifications/sdk_files/(.*)

WP Rocket

In the WP Rocket CDN settings, under "Exclude Files From CDN" add the following line:

(.*)/onesignal-free-web-push-notifications/sdk_files/(.*)

Then press save.

LightSpeed Cache

In the LightSpeed CDN settings, under "Exclude Path" add the following line:

(.*)/onesignal-free-web-push-notifications/sdk_files/(.*)

Then press save.

WP Super Cache

Log in to your WordPress admin panel and visit Settings > WP Super Cache.
Click the CDN tab.
Make sure the Exclude if substring tab has at least the following contents: .php, onesignal-free-web-push-notifications. You can have more than this, but you must have at least these two entries.
Click the Contents tab.
Click the Delete Cache button.
The required files should now be served from your domain. Refresh your site page.

WP Engine

In your WP Engine plugin > General Settings > HTML Post-Processing

add the below URLs replacing "YOURSITEHERE" with your website:

#https?://(www\.)?(YOURSITEHERE\.com|mywpenginehandleHere.wpengine.com|wpengineCDNpathHere.wpengine.netdna-(ssl|cdn).com)/wp-(content|includes)# => https://wpengineCDNpathHere-wpengine.netdna-ssl.com/wp-$4
#https://wpengineCDNpathHere-wpengine.netdna-ssl.com/plugins/onesignal-free-web-push-notifications/# => https://mywebsiteHere.com/wp-content/plugins/onesignal-free-web-push-notifications/
#https://wpengineCDNpathHere-wpengine.netdna-ssl.com/wp-content/plugins/onesignal-free-web-push-notifications/# => https://mywebsiteHere.com/wp-content/plugins/onesignal-free-web-push-notifications/

W3 Total Cache

Log in to your WordPress admin panel and click Performance on the left sidebar.
Click the CDN tab.
Find the textbox for "Rejected files".
Add an entry for {plugins_dir}/onesignal-free-web-push-notifications/sdk_files/*
Click Save all settings.

BunnyCDN

Add OneSignal to the excluded phrases in the BunnyCDN plugin under the advanced settings.

Once that's saved, purge the HTML cache if you're using any HTML caching plugin such as WP Total Cache.

CDN Enabler

Log in to your WordPress admin panel and click Settings -> CDN Enabler on the left sidebar.
Find the "Exclusions" textbox.
Add "onesignal-free-web-push-notifications".

Your textbox might look like ".php,onesignal-free-web-push-notifications".
Click Save Changes.

PressCDN

In the PressCDN settings under Exclude Directories add: /wp-content/plugins/onesignal-free-web-push-notifications/

Breeze

In Breeze > Settings > CDN > Exclude Content add /onesignal-free-web-push-notifications/sdk_files/

Hummingbird Pro

In Hummingbird Pro > Asset Optimization find "remote_sdk" with "OneSignalSDK.js#asyncload"

Select that file and remove from Optimization.

Then reset any cache plugins and return to the site.

Security Plugin Issues

Sucuri

Sucuri provides an option in its settings to whitelist files. Please see Sucuri's Whitelist File or Folder guide.

iThemes Security plugin

Uncheck "Disable PHP in Plugins" option under "System Tweaks" or "System Modifications"

Defender Security plugin

Make sure you do not "Prevent PHP execution" in your settings.

Defender Plugin > Security Tweaks > Do not "Prevent PHP execution.

Example .htaccess

<Files *.php>
Order allow,deny
Deny from all
</Files>
<Files OneSignalSDKWorker.js.php>
Allow from all
ForceType 'application/javascript; charset=UTF-8'
</Files>
<Files OneSignalSDKWorker.js>
Allow from all
ForceType 'application/javascript; charset=UTF-8'
</Files>

Server slows down or website becomes unreachable upon a notification being sent

This can happen for a few reasons. The below options are ways to help prevent it from occurring. If you continue to see issues, you may need to contact your host provider and upgrade your bandwidth or ask for additional assistance on what is causing this issue.

Don't host your own notification icons

If you are hosting your own images and are using them in your notifications, the your server could be overloaded for requests for that image. This doesn't require users to click the notification as the image must be queried in order to actually display it in the notification.

SDK Worker Files

If you are not hosting your own images but continue to see significant slow-downs when notifications are sent, chances are the problem is that browsers are fetching four specific files from your server:

OneSignalSDKWorker.js.php
OneSignalSDKWorker.js

These files should be publicly accessible. See our OneSignal Service Worker FAQ for more info.

These service worker files are required for showing push notifications. Browsers will try to refresh them by fetching the files from your server if it has been more than 24 hours since the last refresh. Depending on how many subscribers you have, this can be taxing on your server.

There are several solutions to this issue:

Solution 1 - Set up a CDN

You can set up a free Cloudflare account which can cache these files as well as other pages on your site to greatly lower the load on your server.

Solution 2 - Throttling

Enable Throttling which allows spreading out the sends over time. Paid plan required.

Solution 3 - Update Service Worker Files Path

These 2 service worker files go into PHP instead of served as a static file from your host. This plugin uses PHP since a HTTP header needs to be added if the service worker files can't be put on the root of your site which plugins don't have access too. The OneSignal WordPress plugin does not have an option to configure this in the UI however if you can upload some files to the root of your site and can add some javascript to your WordPress template you can use static files.

Upload OneSignal Service Worker files (download the files here) to the root directory of your WordPress site. should be accessible like this:

https://yoursite.com/OneSignalSDKWorker.js

In the WordPress Admin go to OneSignal Push > Advanced Settings and turn on "Disable OneSignal Initialization".
Add the following custom code to your WordPress template

<script>
  window.OneSignal = window.OneSignal || [];
  window.OneSignal.push(function() {
    OneSignal.SERVICE_WORKER_UPDATER_PATH = "OneSignalSDKWorker.js";
    OneSignal.SERVICE_WORKER_PATH = "OneSignalSDKWorker.js";
    OneSignal.SERVICE_WORKER_PARAM = { scope: '/push/onesignal/' };
    delete window._oneSignalInitOptions.path
    window.OneSignal.init(window._oneSignalInitOptions);
  });
</script>

<script>
  window.OneSignal = window.OneSignal || [];
  window.OneSignal.push(function() {
    OneSignal.SERVICE_WORKER_UPDATER_PATH = "wp-content/plugins/onesignal-free-web-push-notifications/sdk_files/OneSignalSDKUpdaterWorker.js";
    OneSignal.SERVICE_WORKER_PATH = "wp-content/plugins/onesignal-free-web-push-notifications/sdk_files/OneSignalSDKWorker.js";
    OneSignal.SERVICE_WORKER_PARAM = { scope: "wp-content/plugins/onesignal-free-web-push-notifications/sdk_files/" };
    delete window._oneSignalInitOptions.path
    window.OneSignal.init(window._oneSignalInitOptions);
  });
</script>

This should lower CPU and memory usage as users return back to your site however this will be a slow process. Depending on how static files are hosted on your site however, this might still not be enough. This is why we recommend using a CDN such a CloudFlare as you can configure this to completely cache these file for you.

Notifications Not Being Sent

No Recipients Error

If you are JNews Theme, go to JNews > Install Plugins > Desktop Push Notifications > Deactivate JNews - Push Notifications. More details here.

Debugging with Gutenberg

Turn on debug():

Open the Dev Tools Console. To open the console, right click on the page, click Inspect, and click the Console tab.
While in the editor page, type OneSignal.debug() into the console. Hit ENTER. You should see undefined returned on the line below.
Publish your post/article. You should see some debug data display in the console. If you click on the response_body, you should see three values: 1) id, 2) recipients, and 3) external_id.

Update Service Worker Scope

In the WordPress Admin go to OneSignal Push > Advanced Settings and turn on "Disable OneSignal Initialization".
Add this code to your site to set the scope

<script>
  window.OneSignal = window.OneSignal || [];
  window.OneSignal.push(function() {
    OneSignal.SERVICE_WORKER_UPDATER_PATH = "wp-content/plugins/onesignal-free-web-push-notifications/sdk_files/OneSignalSDKWorker.js";
    OneSignal.SERVICE_WORKER_PATH = "wp-content/plugins/onesignal-free-web-push-notifications/sdk_files/OneSignalSDKWorker.js";
    OneSignal.SERVICE_WORKER_PARAM = { scope: "wp-content/plugins/onesignal-free-web-push-notifications/sdk_files/" };
    delete window._oneSignalInitOptions.path
    window.OneSignal.init(window._oneSignalInitOptions);
  });
</script>

OneSignal Push: Did not receive a response status from last notification sent

This can be safely ignored, the message has been sent.