You don’t pay with Paypal through Alibaba. You really don’t pay “through” Alibaba. You have the contract created in Alibaba, that will include trade assurance. Then the terms of the contract will give you payment instructions which will include the TT/bank wire or paypal payment information which you can use to pay them. Once you pay you can upload the payment information to Alibaba to get it to go to the next step as the supplier will confirm receipt of payment, etc. Then they ship it out and it goes through the process, and once you confirm on your end that you received the shipment, it will release their funds to them accordingly.