Can you check at those failures, if there are any timeouts??? or if there is any chance you can post the entire flow run, with everything showing, I realize you may need to black some stuff out but it would help a ton.
Also, I would recommend the following
Wrap your Action in a Try / Catch scope error handling, so that when it fails, like this you can try again. I do not know what you have set for retries etc, but I would very much like to validate that
1) the incoming data was properly collected, its possible it wasn't
2) that the proper data was passed to Prompt (which you should be able to also go into Copilot and validate what IT says happened
3) whether it was simply some weird connection issue or timeout.
If its not 1 or 2 and on the Copilot Activity size or Azure AI it said all was good you might get more details.
But if you at least wrap it properly in a Try / Catch, then it will automatically redo it and it won't fail outright unless there is a real issue.
Which I think is what you are trying to get around?
I dont know how many actions and or charges you are facing so I doubt its specifically a "charge" issue, if the rest work. It could just sincerely but load related.
As all my videos etc are still down I am sharing this to review
If this helps or if you can share and we can try to isolate the exact issue it would help.