Hi,
Hmm.. I am wondering if when you are building the App I believe its because the URI / IP is different than when you Play (run it) so I believe you need to
verify that its allowed from the IP / Range of the Run, not the Edit
I hope that makes sense, as thats the only thing I can think of, unless its a user based issue, where I assume its YOU doing the run etc.
What you can try though to get more details.
1. Close the app in Run Mode
2. Go to Apps from Power Apps.com
3. Find your app and select the ...
4. Select Details => Monitor
5. once monitor is up, click Play Published Version
6. Once that tab opens, causey our error to happen
7. Flip back to Monitor and Filter (top right) by Error
8. Now find the "grouping 2-4" of errors related to your specific error
When you do, one of them will open a side window on the right with 4 Tabs. The 4th is the Response
Open the Header and Body of that Tab
Look at the Body and look for more details about the error, it should say more than the above.
If that helps please mark this as the answer, or if you need more help come back.