Boolean expression expected

What causes this issue?

A boolean expression is an expression that is evaluated as true or
false.
The syntax check found an error. A boolean expression is expected at
the cursor.

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 your entry and make the necessary correction. See also the other
possible causes of error (messages).

Error message extract from SAP system. Copyright SAP SE.