A customer demand is about to become time-barred?

In such cases, it can make sense to set up a limitation waiver.

The answer in detail
Most demands become time-barred when the limitation period expires. This is normally three years from the end of the initial year. If you set up a limitation waiver, you can avoid expensive litigation. The limitation waiver merely prevents the demand from becoming time-barred: The demand is therefore not lost and a common solution can be sought with the debtor. Attached you will find a sample limitation waiver.
Important documents
Vorlage Verjährungsverzichtserklärung