Facebook’s in-app browser (on mobile devices) does not support web push notifications. Whenever someone clicks on your ad on the mobile app, the link opens in Facebook’s native browser. Because of this, you aren’t able to get any subscribers from Facebook ads.
Fortunately, Facebook gives you the option to open the link in the default browser of the mobile device. You just need to change one setting while creating your ad.
Here’s how you can go about it:
1. Open your Facebook Business account.
2. Navigate to Ads Manager and Click on ‘Create’ under any of the following tabs: Campaign, Ad sets OR Ads.
3. Click on ‘Catalog Sales’ as your Marketing Objective.
4. Insert all the required details and complete your ad until the final subsection, 'Links.' You will find this under Ads.
5. In the 'Links' subsection, select the drop-down menu for 'App Link Destination' and click on 'Open deep link in a mobile browser' from the options.
6. Submit your ad once you're satisfied.
Now, when visitors click on the ad on their mobile, the link will open on the mobile's default browser. This will ensure that every visit to your store that comes from your Facebook ad has the option to subscribe.
Note: Never run ads to get subscribers for push notifications. Potential customers click on ads because they want to buy a product, not to subscribe to your notifications. Never make subscriptions as the primary goal of your ads. At the most, it’s an added benefit to running an ad. This also applies to other mediums like emails and SMS as well, not just push notifications.