How To Fix V1318 - External number assignment is not defined for document type &

SAP Error Message - Details

• Message type: E = Error

• Message class: V1 - Verkaufsbelegbearbeitung

• Message number: 318

• Message text: External number assignment is not defined for document type &

What causes this issue?

For document type &V1&, no external <GL:number_range>number range</> is
defined. Therefore, external <GL:number_assignment>number assignment</>
is not possible.
INCLUDE 'NA_NO_PROCESSING_2' OBJECT DOKU ID TX LANGUAGE EN
INCLUDE 'NA_CHECK_ENTRY' OBJECT DOKU ID TX LANGUAGE EN
If you want external number assignment to be allowed, you must specify
an external number range for this document type.
INCLUDE 'NA_CUST_MAINTAIN_3' OBJECT DOKU ID TX LANGUAGE EN

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.