Digital signature is not active for interval (&1,&2,&3)

What causes this issue?

You have posted a document that requires a digital signature, but
digital signature generation is not activated in Customizing for the
corresponding number range interval.
Digital signature generation must be activated for documents that are
posted in a Portuguese company code or in a Portuguese organizational
unit of a foreign company code. If digital signature generation has
already started for a particular number range interval, all documents
that use the number range interval must have a digital signature.

System Response

The system prevents the posting.

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

You have the following options:
If no documents were posted for this number range interval while digital
signature generation was switched off, you can switch it back on again
and continue to use the number range interval.
If documents were posted while digital signature generation was switched
off and there are therefore documents without digital signatures for
this number range interval, you can no longer use the number range
interval.
Create a new number range interval for the relevant company code and
fiscal year and switch on digital signature generation. To avoid
inconsistencies in the database, you must use a different combination of
leading document type and series.
Note that digital signature generation can also be deactivated by
entering an incorrect start date or time.

Error message extract from SAP system. Copyright SAP SE.