Structure of segment &1 is unknown (field name &2)

What causes this issue?

The system cannot fully check the structure of segment '&v1&'. The check
of the data element of field '&v2&' returned an error.

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?

Check the consistency of the segment definition using the IDoc
definition tools.

Error message extract from SAP system. Copyright SAP SE.