You should pay the seller after you receive an invoice from them, which includes your grand total and information on where to send payment. There are two ways you will receive the invoice:
Please do not send payment to the seller before receiving your invoice because the total due for your order will need to be updated by the seller with the shipping cost and other charges.
Paying by PayPal:
The seller should provide you with their PayPal e-mail address. You should not send a payment immediately to the seller's e-mail address that's provided on the order notification e-mail, as their PayPal e-mail address may be different than the one that the seller has on file with BrickLink.
To pay the seller, login to your PayPal account, click Send & Request, select Pay for goods or services, and then fill out the seller's provided e-mail address and payment amount. It is a good idea to include your BrickLink order number in the comment section.
Paying via Onsite PayPal:
With this method, the BrickLink ordering system is connected to PayPal. Note that you will only see this option when you buy from stores that enabled Onsite Payment.
To pay the seller, click the “Pay” link in your invoice and enter your PayPal information in the popup window. You can also access the “Pay” button through your Orders Placed page once an invoice has been issued by the seller.
For sellers: To enable Onsite PayPal in your store, click here
Troubleshooting Onsite PayPal Errors
For troubleshooting, please visit our Knowledge Base.