A Simple Code Snippet to check if the provided email in FluentForms submission is a CRM contact and is in a block lists tags.

fluentcrm-contact-check-ff-email-validation.php

<?php

/**
* A Simple Code Snippet to check if the provided email in FluentForms submission is a CRM contact and is in a block lists tags.
* If yes, then it will reject the form submission
*/

add_filter('fluentform/validate_input_item_email', function ($error, $field, $formData) {
    if ($error || !defined('FLUENT_CRM')) {
        return $error; // already an error or FLUENTCRM is not activated
    }

    $inputName = \FluentForm\Framework\Helpers\ArrayHelper::get($field, 'raw.attributes.name');
    $inputEmail = \FluentForm\Framework\Helpers\ArrayHelper::get($formData, $inputName);
    $crmContact = FluentCrmApi('contacts')->getContact($inputEmail);

    $blockListTagIds = [1, 2]; // change the tags IDs
    if ($crmContact && $crmContact->hasAnyTagId($blockListTagIds)) {
        $error = [
            'email_blocked' => __('The email address you have entered is blocked from submitting this form.', 'fluentform')
        ];
    }

    return $error;
}, 10, 3);