Index series & not allowed (Check your entry)

What causes this issue?

Index series &V1& has not been defined.

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?

You have the following choices:
Use a defined index series (Possible entries F4)
Define an index series using the Customizing functions.
<DS:TRAN.OAV5>Proceed</>

Error message extract from SAP system. Copyright SAP SE.