Namespace of user is &1. Please assign User to Namespace &2.

What causes this issue?

You want to change an item with namespace <(>&<)>2 but your user is
assigned to namespace <(>&<)>1.

System Response

A change of items with namespace <(>&<)>2 is not allowed as long as your
user is not assigned to this namespace.

How to fix this error?

Please go to the app Extensibility Settings and assign your user to
namespace <(>&<)>2

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.