How to work with Google wallet api?

Question

Google

I ask for help, since I can’t solve the problem for more than a day,
at the final stage a request comes from Google wallet, the payment goes through, but Google reports that POSTBACK_ERROR and an error description that the seller’s server did not respond to the request, although at the final stage a notification is received to the url specified in the wallet settings, and my server responds with HTTP 200, and the correct data (specified when requesting sellerIdenifier , key, etc.) i.e. the data sent, matches those sent from Google.
Guys, can anyone come across? I'm already tired.