No internal key found for the PSP element & in field &

What causes this issue?

An external name for a PSP element has been transferred in field &v2&.
The external name should be converted to the internal data base key. No
internal PSP element numbers could be found for plant &v1&.

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?

Check the transferred value.
Does the PSP element exist in the system?
Has the external name of the PSP element been transferred correctly,
for example, without any formatting?

Error message extract from SAP system. Copyright SAP SE.