Constant expected (expression '&1', position &2)

What causes this issue?

A constant is expected in expression &V1& at position &V2&. However, the
specified (part) expression is not a constant.

System Response

The expression contains a syntax error and must be corrected.

How to fix this error?

Specify a constant using the delimiter characters '...' or "...".

Procedure for System Administrators

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

Error message extract from SAP system. Copyright SAP SE.