"Unexpected error" while editing an "Offsite payment provider" extension.

Hello team,
We have created a new Shopify app with an “Offsite payment provider” extension. The issue is that when editing the draft version of this extension and trying to set the “Payment Methods” by clicking on the “Add payments methods” button, we’re getting the following error message:

Unexpected error
We have encountered an unexpected technical issue.
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Any ideas when this is going to be fixed?