mepr-validate-user-role.php

<?php

function mepr_validate_user_role($errors) {
  // Memberships to apply restrictions on.
  $membership_ids = array('123', '321', '12345');

  // The current membership isn't being validated, so don't do anything else.
  if(!in_array($_POST['mepr_product_id'], $membership_ids)) {
    return $errors;
  }

  $current_user = wp_get_current_user();

  if($current_user->ID == 0) {
    $errors[] = 'You must be logged in and have the MICHA Member user role to sign up.';
  } else {
    // Check if the user has the MICHA Member role.
    if(!in_array('micha_member', (array) $current_user->roles)) {
      $errors[] = 'You must have the MICHA Member user role to sign up.';
    }
  }

  return $errors;
}
add_filter('mepr-validate-signup', 'mepr_validate_user_role');