Regex validation

Hello,

Nice plugin, but a question about working with regex. How would i implement this in the RegEx pattern field? I’ve got a fairly simple zipcode checker for the netherlands as follows:

/^[1-9][0-9]{3} ?(?!sa|sd|ss)[a-z]{2}$/i

Which works fine on regex101, but i can’t get it working on a single line text field. The custom error message keeps popping up like i entered a wrong value.

Any suggestions are welcome.