Wage type &1 must be in table &2 to perform offsetting on &3

What causes this issue?

During the fourth processing phase of GBSXP, Statutory Absence Table
PC27J (MSA) entries have the OXP and Full Pay information added. (This
only happens if there are MSA entries.)
For each MSA entry, the OXP entries are derived from the feature COVER
(Determine Rule Group for the Refinement of Absences). The valuation
rules from COVER are then cross-referenced to table <ZK>Absence
Valuation</> (T554C) to derive which wage types should be in the Input
Table PC207 (IT) for the current period (or ORT, if we are looking at
the previous period).
The international payroll function PAB (Valuating Absences) only
creates entries on working days/hours if the customising specifies
working hours/days instead of calendar days. In this case, no check is
performed on non-working days after the application of Note 603847.
If however, you have managed to remove a OXP wage type from the IT (or
ORT) before GBSXP is processed, then this error message will be raised.

System Response

A permanent error has occurred during the processing of the payroll for
this employee. Payroll processing for the employee has been terminated.

How to fix this error?

This error is due to an error in the customising of your payroll
subschema for "Up to Gross" (that is, your copy of subschema GT00). You
should check whether:
1) You may have mistakenly put in a customer specific PCR before GBSXP
that has moved the wage type to RT, or
2) You may still have the redundant Personnel Calculation Rule GAB4 in
your schema, but before GBSXP.

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.