Provision account key missing for condition type &1 in schema &2

What causes this issue?

Condition type &V1& is marked as "provision-relevant". However, the
account key for posting provisions is missing in schema &V2& for this
condition type.
It is not possible to make a posting to the provision account without
an account key.

System Response

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

How to fix this error?

Maintain the provision account key for the condition type in
Customizing for Purchasing.

Procedure for System Administrators

Error message extract from SAP system. Copyright SAP SE.