Capacity & not available

What causes this issue?

The system could not find any remaining available capacity within the
planning period.

How to fix this error?

Increase the planning period or
increase the available capacity &V1& or
reschedule a commitment which already exists for the capacity &V1& or
check whether the formulas in the work center for calculating the
duration or capacity requirements lead to different results. For
example, if the capacity requirements calculated are twice that of the
duration, then two capacities are required. In this case, you should
increase the available capacity or change the formulas.

Error message extract from SAP system. Copyright SAP SE.