Hi Three Sons,
Thank you very much for your answer.
I have already tried this and backbone is loading perfectly.
During debugging I forgot to disable our theme. With the pure Twentytwenty theme it works. So it’s the theme, what exactly is the problem there, I can’t say.
My workaround was to write API keys directly into the mysql database. Is there anything wrong with that?
Thanks for the help and greetings
Chris