Mollie technically calls a hook when it processes the request. As I found out the hard way, it doesn't always do this so it will be a good idea to process the transaction IDs manually and double-check and not just rely on the hook. The following transaction status are calling the hook URL:

• open: no hook
• cancelled: hook
• pending: no hook
• expired: hook
• failed: ?
• paid: hook
• paidout: no hook!!
• refunded: hook
• charged_back: ?

More info on this is at https://www.mollie.com/en/docs/status