I too got the message "There was an error processing your request. Please try again later".
But on inspecting the issue in the browser DevTools got the error to be: "ENTITY_UNPROCESSABLEMISSING_BETA_APP_DESCRIPTION"
Go to AppStore Connect app on the mobile and try again.
On reaching the step to add builds, it gave me the warning that the Beta App Description is not set and a button to go to the screen and fill it up.
The comment from greensopinion is what saved me.
Jun 23
I've encountered the same issue. For a workaround, I was able to submit the build to TestFlight using the AppStore Connect app on my iPhone instead of using the website.
Ritesh-Turgajo
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