Possibility of Custom Field Validation?

Hi I am in the process of rebuilding an already made form. We used Nex-Forms to start, and have a license from Nex-Forms. I know there is validation built in to each field. We have a field which should take zip codes. However, I only want the user to be able to succeed if they input a valid zip code from an array, any other zip code I want to display an error. I have generated some javascript which should be able to accomplish this. I have removed the zip codes that I have, while testing, and have not modified the next button ID to reflect the actual form from testing.

document.addEventListener('DOMContentLoaded', function () {
// Allowed zip codes
var allowedZipCodes = [
'00000'
];

var zipCodeField = document.getElementById('nFormZipCode');
var nextButton = document.getElementById('nextButtonId');

if (zipCodeField && nextButton) {
    zipCodeField.addEventListener('input', function () {
        var zipCode = zipCodeField.value.trim();
        if (allowedZipCodes.includes(zipCode)) {
            zipCodeField.setCustomValidity(''); // Valid input
            nextButton.disabled = false; // Enable Next button
        } else {
            zipCodeField.setCustomValidity('Invalid zip code.'); // Generic invalid input message
            nextButton.disabled = true; // Disable Next button
        }
    });

    // Initially disable the next button
    nextButton.disabled = true;
}
});

I can’t find a place to insert this without the form validation at form submit. Is there a way to have validation on the “next” button?

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