Migrate DC to Cloud Error: The base URL did not validate

Hi, I’m trying to make a test run to migrate data from our app from DC to Cloud. When I try to setup the migration using the Migration Assistant from the DC Jira, I get to the step to choose the Cloud destination. Once I enter the url of the DC Jira in the “migrate from” field, I’ll always get the error “The base URL did not validate” (see screenshot).

The URL is valid and the Jira is running properly. Why does it not work?

cheers Moritz