Transaction/event type & does not exist

What causes this issue?

The system was not able to find the
<GL:transaction/event_type>transaction/event type</> you entered.

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?

INCLUDE NA_EINGABE_PRUEFEN
If you do not know the transaction /event type, press <LS>F4</>
(possible entries) in the <LS>transaction/event type</> field.
You can also check whether the desired transaction/event type has been
maintained for the number ranges.
<DS:TRAN.OMBT>Display number range groups</>

Error message extract from SAP system. Copyright SAP SE.