As usual, google decided to integrate something new breaking everything in the process...
Just received the requirement to update my project to a new billing API(to 7) and SDK(to 34) if you have problems, like I had, here is how I fixed everything(at least there are no errors during the upload to google play):
I am using UE5.1 for my project, target SDK change is still should be performed in the manifest file (look how it is done here) I recommend setting target Target SDK Version to 35
And for the billing info:
I edited the file OnlineSubsystemGooglePlay_UPL.xml
it is in the folder UE_5.1\Engine\Plugins\Online\Android\OnlineSubsystemGooglePlay\Source
there I changed line com.android.billingclient:billing:5.0.0
to com.android.billingclient:billing:7.0.0
(actually don’t think this helped but changed for good measure)
In the manifest file from Target SDK change I have added the line com.android.billingclient:billing:7.0.0
(I believe this is what helped)