I have a Facebook app (canvas app), let's say https://apps.facebook.com/test, that redirects and works as expected on the desktop (on all browsers that I have tested).
On mobile phones (both from the FB app and the browser) the path gets redirected to https://m.facebook.com/apps/test/?ref=web_canvas, which gives a "This page cannot be found" error. Why?
This has been reported as a bug to Facebook and Facebook has confirmed it as a bug. They have not provided a date on when the fix will be ready.
You can follow the status of the bug here: https://developers.facebook.com/bugs/1051463851558493/
Update: Facebook have (since the information struck-out below) completely removed support for this. The thread about this is here:
https://developers.facebook.com/bugs/1051463851558493/
The top-level information is:
We have now deprecated Mobile Canvas URL. This means that you will no longer be able to direct to a website/app directly within the Facebook mobile web based upon the external destination URL you have specified in the 'Mobile Site URL' field for the app on developers.facebook.com. Furthermore, we have removed the 'Mobile Site URL' field from the app setup going forward. This deprecation also applies to apps that were previously whitelisted.
So it's time to move away from this functionality, and either integrate the newer FB Instant Games functionality or just link to an external website as having your canvas app hosted inside the FB mobile app simply isn't possible as it was in years gone by.
Facebook has disabled mobile URLs working by default:
We recently identified a handful of apps misusing our mobile App Center to redirect people to unauthorized sites. As a precaution, we have temporarily turned off the ability for developers to direct to a destination URL for any app in the "Mobile Site URL" field on the dev site.
Now if you wish for this functionality to work, you need to be logged into Facebook and then go to the following URL:
https://www.facebook.com/help/contact/588209321338256
This URL will effectively put your request in a queue, for someone at Facebook to manually verify your app configuration isn't malicious, and then enable the redirection. I do not like posting this answer, as I know it will eventually become invalid, but as of today it is the only answer. As stated by Scott, you can follow progress on this issue here:
https://developers.facebook.com/bugs/1051463851558493/
Please ignore the fact it claims the issue has been 'Fixed' as Facebook count the above workaround as a fix. If you read through the comments on the bug you can note the waiting time to get the URL fixed (on a per app basis) is typically several weeks.
On May 28th, 2017, Facebook confirmed that the Mobile Canvas URL has now been deprecated. Any apps already using (and white listed) will stop working, and no new apps will be accepted.
Hi everyone,
First, please accept my sincere apologies for the delay in getting back to you with an update on the status of Mobile Canvas URL. I understand your frustrations, particularly if you submitted your details via the form and were waiting on a response.
We have now deprecated Mobile Canvas URL. This means that you will no longer be able to direct to a website/app directly within the Facebook mobile web based upon the external destination URL you have specified in the 'Mobile Site URL' field for the app on developers.facebook.com. Furthermore, we have removed the 'Mobile Site URL' field from the app setup going forward. This deprecation also applies to apps that were previously whitelisted.
The Mobile Canvas URL feature is a vestige of a long ago deprecated product called Mobile Canvas. Facebook maintains a high commitment to quality, so we don't want to leave unsupported products active — especially when they continue to cause bugs for our developers. Going forward, we're recommending you take advantage of the well-supported Facebook Games on Web product to drive traffic to your app.
We've also introduced Instant Games which lets people play mobile games within Messenger and Facebook News Feed. We invite you to sign up for our closed beta program. We believe letting people play games together on Facebook is a powerful experience for both players and developers.
If your app is still set up to rely on Mobile Canvas URL functionality, we recommend taking the following actions:
If you're using Mobile Canvas to link to a page on mobile web, you need to update your app to handle the redirection in the desktop iframe. User interaction is required to redirect away from web canvas as our Platform Policy does not allow automated redirects from canvas.
If your app was previously whitelisted, you will need to take action as this deprecation supersedes any workarounds you have in place.
Thank you for your understanding as we continually improve the products and services we offer to both developers and players. Again, please accept my apologies for the wait in getting back to you with this information
Best regards,
Tim
See this thread https://developers.facebook.com/bugs/1051463851558493/