IDoc status &1 cannot be set (see long text)

What causes this issue?

You can only set the following status fields using manual linking:
<ZH>53 </> Application document posted
<ZH>68 </> Error - no further processing
You do not have to set a new status value, which means that the
existing status 51 can stay as it is. This enables you to link the IDoc
with several transactions and only assign 'Completed status' (53, 68)
at the end.

Error message extract from SAP system. Copyright SAP SE.