Check off the total and fixed field groups in the same currency

What causes this issue?

You have checked off a total cost field group and a fixed cost field
group for manual maintenance. However, the currencies of these two
field groups are not the same. This is not allowed.

System Response

The system rejects the entry.

How to fix this error?

Check off the fixed cost field group in the same currency as the total
cost field group, or vice versa.

Error message extract from SAP system. Copyright SAP SE.