I have tried like 10 variations of this, so I feel like I am missing something.

I am trying to make Oppo_Waveitem required if the first 3 characters of the oppo_description doesn't equal 'OTF' but no matter what i try it doesnt work. I am doing this as a validation script. Any ideas? Thanks!

var soppoOTF = Values('oppo_description').substring(0, 3);
if (soppoOTF === "OTF") {
Required = true;
}