Formula cannot be saved because it contains syntax errors

What causes this issue?

You have attempted to store a formula that has no syntax errors but is
not yet complete.

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

System Response

How to fix this error?

Complete the formula so that the status light is "green" and save the
formula once again, or exit the Formula Builder through the "cancel"
function, without saving changes.

Error message extract from SAP system. Copyright SAP SE.