I am using the below hook to create a random membership

I am using the below hook to create a random membership number for users which is saved as user meta and displayed on the account page.

add_action("membership_add_subscription", "create_membership_no", 10, 2);

It works for subscription levels which have price set to £0.00 but when testing live using paypal express for £0.01 it does not seem to work. Is there a paypal success hook I can try or is there something else?