When I click the "Check URL" button after setting the callback URL after registering a reward ad, I get an error message "An internal error occurred, please try again later".
When I tested the same address in browsers (Edge, Chrome, Safari), I was able to receive a success code (200) as normal.
There are no access logs from the server, so it appears that the request was never even sent.
Note that the source was still working fine, just the URL was changed on the server.
I tried to find a solution via this link:
validate rewarded ad views with server side verification but couldn't find it, so I'm leaving an inquiry.