Store stripe info as user_meta

Sounds like the $amount variable is empty so it’s not saving. Echo it out to see what’s happening.

Make sure the $payment_user_id is an actual WordPress user_id.

Wrap your update_user_meta within the if statement.

// If charge is successful, store in user meta
if (isset($event) && $event->type == "charge.succeeded") { 
  $amount = $event->data->object->amount / 100;

  echo $amount . ' <- $amount';

  $payment_user_id = 9192321; 
  update_user_meta($payment_user_id, 'payment_history', $amount);
}