Blacklist specific tld emails of WPForm's email field

wpforms-restrict-tld-emails.php

<?php

/*
 * Blacklist ru tld emails from your WPForms.
 *
 * @link https://wpforms.com/developers/how-to-restrict-email-domains/
 *
*/

function wpf_blacklist_ru_domains( $field_id, $field_submit, $form_data ) {
    $tld        = substr( strrchr( $field_submit, "." ), 1 );
    $blacklist  = array( 'ru' ); // add the TLDs here. 

    if( in_array( $tld, $blacklist ) ) { 
        wpforms()->process->errors[ $form_data['id'] ][ $field_id ] = esc_html__( '.ru emails are not accepted.', 'wpforms' );
        return;
    }
}
add_action('wpforms_process_validate_email', 'wpf_blacklist_ru_domains', 10, 3 );