Maintain number assignment for &

What causes this issue?

In cost accounting, postings from other SAP modules are written to
separate documents. The SAP System cannot assign numbers to these
documents because number assignment is not defined in &V1&.

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 whether object &V1& was defined in table TNRO and contact the SAP
hotline service.

Error message extract from SAP system. Copyright SAP SE.