Facebook Marketing API asset access suddenly denied

I was experiencing the same thing. As Pieter suggested, it look like it was a bug and has now been resolved. My app is working fine now.

Seems to be an issue with Facebook as I'm currently experiencing the same thing. I'm not using PHP though, using Node on this side.

I just had the same issue. I was able to resolve it by changing the status of the app from 'Off - In Development' to 'On - Live'. After going live I was not able to find my app by searching for it. If that changes because of some delay on Facebook's end I'll update this.

Update: According to https://developers.facebook.com/docs/apps/managing-development-cycle/ it doesn't look like your app can be found unless you submit it to the App Center.

I hope this works for some of you.

1) I was able to resolve the problem navigating to the following domain containing the app settings.

https://developers.facebook.com

2) Under "My Apps", select your app (mine was in dev mode).

3) Then select the "advanced" settings in the left-hand margin. See image below.

4) On the next page, I scrolled down to the Business Manager subsection and selecting my company. Saved the changes on the page. At the time my Facebook Account was an Admin for this business.

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Then ran my Python Script. Everything worked afterwards.

My app was in dev mode the entire time as we only use it internally.