Internal assignment of sub numbers - passed number &1 will be ignored

What causes this issue?

An entry with a value was passed on for the internally assigned
subnumber in a (B)API call.

System Response

This value is ignored for the corresponding entry. A new internal number
is used instead.

How to fix this error?

If you want to refer to a new entry - for example, by assigning a
dominant parcel for a new easement entry - you need this number (which
is assigned later) to reference the new entry when you call the (B)API.
You can enter a "Mapping Number" for this. This number must be in an
area above '900' and is also ignored on creation. A mapping table is
supplied with these numbers, however, in order to create a reference to
the internal number actually assigned.

Procedure for System Administrators

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.