Quit argument error

Use 'Return' instead: https://docs.intersystems.com/irislatest/csp/docbook/DocBook.UI.Page.cls?KEY=RCOS_creturn

In general, if you're trying to exit a method and return a value to the caller, 'Return' is the best way to do that, as 'Quit' also has functionality for control flow (such as breaking out of WHILE loops).

The Quit command is quitting the if statement therefore no value is allowed.

Clean code is not to have multiple places that quit with value, in long code it is difficult to track. Therefore a nice structure could be:
Ser result=1
If [condition] { ... set result=0 }
else { ... set result=1 }
Quit result