Update Select Option in User Profile

I’m trying to update a selection option “dropdown” in a user’s profile with a particular value once they complete an action.

I’m able to do this just fine with “input” fields in the user meta but can’t figure out the syntax to update a dropdown value.

Here is what I have, where “payment_type” is the name of the ID of the user profile field I created:

$custom_fields = get_user_option('s2member_custom_fields', $payment_user_id);
$custom_fields['payment_type'] = 'Stripe';
update_user_option($payment_user_id, 's2member_custom_fields', $custom_fields); 

Again, this works for input fields, just not for dropdowns.

Any help would be much appreciated!

I would suggest to create s custom dropdown to see how it will be saved in DB, and then you will be able to reproduce it with your custom values.