The intervals for period &1 overlap

What causes this issue?

The system issues an error message and will not allow you to continue with this transaction until the error is resolved.

System Response

How to fix this error?

Correct the intervals for the period key and make sure that they no
longer overlap. Otherwise, this nonpermissible combination could lead
to incorrect expected values and calculations for extrapolation,
proration, and budget billing amount calculation.

Error message extract from SAP system. Copyright SAP SE.