Local packages do not belong to a transport layer

What causes this issue?

You attempted to assign a local package, whose name begins with 'T' or
'$', to a transport layer. Objects belonging to local packages are
however not transported.

System Response

The local package is not assigned to a transport layer.

How to fix this error?

Also refer to the documentation on <DS:DE.DEVCLASS>packages
</>.

Error message extract from SAP system. Copyright SAP SE.