Extended transport control is not active: Cannot specify target client

What causes this issue?

Extended transport control is not active. This means that you can only
release transport requests for the following transport targets:
Target group
SAP system <ZH>without</> specifying a client

System Response

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

How to fix this error?

Change the transport target of the request by removing the client (for
example, "C11" instead of "C11.010").
The simplest way of doing this is to use F4.

Procedure for System Administrators

Error message extract from SAP system. Copyright SAP SE.