Using fieldOptions with Custom Fields
As I haven't seen your code, I can only suggest what worked for me:

function myext_civicrm_fieldOptions($entity, $field, &amp;$options, $params) {

  if ($entity == 'Contribution') {
    if (isset($field) &amp;&amp; $field == 'mycustomfield_123') {
      $myArray = [
        1 =&gt; 'Title 1',
        2 =&gt; 'Title 2'
      ];
      $options = $myArray;
    }
  }
}