Unable to determine pool category for requirement

What causes this issue?

In Customizing for PAM, you define activity types for each pool category
for each controlling area.
When settling a PAM requirement, the system calculates the service
performed for the activity types defined for 'Rental price' and '
Price/unit.'
The pool category is determined using the equipment or message (in this
order) for the requirement
The controlling area is determined from the equipment.
Unable to determine a pool category for the requirement.

System Response

The settlement of the requirement is terminated.

How to fix this error?

Depending on the business process, store a pool category in the
equipment or the message.

Procedure for System Administrators

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

Error message extract from SAP system. Copyright SAP SE.