What causes this issue?

The implementation of method &V1&, which is required for the
calculation, does not exist for calculation module &V2& &V3&, which is
defined in table V_T7PBSCA1A.

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?

If the module is a standard SAP module and the class is a standard SAP
class, contact the SAP Support Line.
Otherwise, ensure that the method specified for your calculation module
is implemented. You can use the examples of the standard calculation
modules to help you do this.

Procedure for System Administrators

Error message extract from SAP system. Copyright SAP SE.