Invalid namespace for &1

What causes this issue?

As per cloud framework guideline, a customer record cannot be created
with SAP reserved pattern. This restriction is implemented to protect
the customer data because if same records are delivered by SAP in future
releases then customer created records will be overwritten.
Namespace restriction is applied on the key fields of an application.
Customers cannot create records starting with below mentioned SAP Best
practice content namespace restrictions.
SAP reserved character fields - S, Q, R, X, P, Y
SAP reserved numeric fields - 5, 6, 7, 8, 9, 0

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

System Response

How to fix this error?

If customer must create the entries with SAP reserved patterns for a
business reason, then corresponding entries in the /SMB/EXM_TABLES
should be maintained to exclude the namespace checks for an application
in cloud.
SAP NOTE for namespace guidelines:
https://launchpad.support.sap.com/#/notes/0002326112

Procedure for System Administrators

Error message extract from SAP system. Copyright SAP SE.