IDoc SOAP Namespace - Violation (&)

What causes this issue?

This IDoc was sent using the SOAP protocol, with the namespace <ZH>
'urn:sap-com:document:sap:idoc:soap:messages'</> used for the SOAP
request.
The following rules apply to this namespace:
A SOAP request can contain one IDoc only and you cannot send multiple
IDocs in a single request.
A system can receive each IDoc only once ("Exactly Once" behavior). This
is guaranteed by using a unique message ID, passed in the field <LS>
ARCKEY</> (ID, key of the EDI archive) of the control record. The
message ID must contain the prefix <ZH>'urn:sap.com:msgid='</>.
The rules above were violated as follows: (&v1&).
Possible error situations:
<ZH>MULTIPLE_IDOCS_NOT_ALLOWED</> The SOAP request contains multiple
IDocs.
<ZH>SOAP_MSGID_INITIAL</> The message ID is missing in the control
record.
<ZH>SOAP_MSGID_PREFIX_INVALID</> The message ID does not contain the
requested prefix.
<ZH>MSGID_LOCKED</> The processing of an IDoc with the same message ID
was already started by another call.

System Response

The IDoc was not accepted by the receiver system.

How to fix this error?

The system issues an error message and will not allow you to continue with this transaction until the error is resolved.

Procedure for System Administrators

Error message extract from SAP system. Copyright SAP SE.