Number of master record & not within external number range

What causes this issue?

You wish to create a service master and have assigned a key for it.

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

System Response

This key does not lie within the reserved number interval that is
derived for this master record from the service category.

How to fix this error?

Check via Customizing (number ranges, service master) which number
intervals have been created for the service category.

Error message extract from SAP system. Copyright SAP SE.