I very much doubt that the generic Chinese adapter you bought, which appears to be designed for home amplifiers, would ever work with your Becker Europa.
Perhaps this would do what you want; it claims to work with the Europa, and it's from one of our trusted suppliers:
https://www.authenticclassics.com/DIN-Plug-Bluetooth-Adapter-for-Stereo-Becker-Radio-p/auth-007527.htmI use a similar adpater designed for my much older Becker Mexico (5-pin DIN, mono) radio, where I have a special button ("Q") to select tape (i.e., DIN connector) input.
-David