Trying to save GF donation amount to ACF custom user field

update-custom-user-field-with-donation-amount.php

<?php 
add_action("gform_after_submission_6", "update_usar_sponsorship_amount", 10, 2);

function update_usar_sponsorship_amount($entry, $form) {
  // get required GF fields
  $team = rgar( $entry, "14"); // GF radio buttons (select Team to sponsor)
  $amount = rgar($entry, "2"); // donation amount

  // query through users
  $users = get_users();
  // loop through users
  foreach ( $users as $user ) {
      $userteam = $user->display_name;
      $currentAmount = $user->sponsorship_amount;
      // $amount = $currentAmount + $amount; // this doesn't work because $amount isn't a number

      // if selected Team name matches user display name, update that user
      if ( $userteam == $team ) {
        update_user_meta( $user->ID, 'sponsorship_amount', $amount );
      }
  }
}

?>