Check on (Bank)account when adding an AP Invoice

Dear all,

I'm trying to make SAP (via B1 UP) validate if the (bank)account of the BP is filled when adding or updating an AP invoice. This will make our payment-process more efficient.

I'm having difficulties with the SQL which I have to add as SQL Condition in the B1 UP Validation Configuration (the action which start the UF: showing a message).

I have till now:

IF (SELECT T0."DflAccount" FROM OCRD T0 WHERE T0."CardCode" = $[$4.0.0]) = ''
BEGIN
SELECT 'SHOW_ERROR' FOR BROWSE
END

When I test the validation, SAP gives me a syntax error of the SQL. I'm doing something wrong, but I don't know what.

Could you help me?

Thanks in advance!

Greets,
Jakob