First of all: almost every German is "in the SCHUFA" - this is not critical at all. It just means that data is available. Over 90% of all people "in SCHUFA" only have positive entries.

If you do not pay bills, this may affect your score at some point, but this will not happen in the short term. We only receive notification of a payment default if two reminders have been sent and the first reminder was sent at least four weeks ago at the time of the notification to SCHUFA.

Paying an invoice late or receiving a reminder does not affect the score. However, if a justified claim has not been settled, the entry remains for three years after settlement.