Bell Ring suppression not working

I’ve got a STR HT2002/2 and it works quite nice with the nuki opener. Unfortunately, the suppression of the intercom ring tone does not work. I have checked the wiring several times but it is definitely correct and the opener has been running for about 10 months without any problems - just without the ring suppression functionality. How can I fix that problem?

I’ve read that in some cases another cable matching solves the problem - maybe in my case, too?

Thank you for your support!

Best regards