Ajax Callback to Update Select List not Working
just got this sorted out! Decided to drill down to the array structure of the form, and found out that the #ajax element had to be attached to the widget array of the field, like this...
$form['product_line']['widget']['#ajax'] = [...]
Now it works. Another reason I keep crying &quot;better documentation for Drupal&quot;!!! How in the world was anybody supposed to know that for existing form fields, this was the format for adding Ajax?!!! Oh well, thanks community  for pointing in the right direction. Anybody knows the right place to insert this in the existing documentation? Cheers all.