Below is a guide on how to pay via paypal. FOR BOTH PAYPAL USERS AND NON PAYPAL USERS.
1. Click on the proceed to checkout button from the parts bin.

2. If you use paypal enter your details in the email and password fields and follow the process to complete payment. If you DO NOT use paypal follow the below instructions.

3. After clicking the ‘Pay by Debit or Credit Card’ you can enter all your details in the fields shown.
IMPORTANT – make sure you untick the create an account toggle if you do not want a paypal account.
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Finally you will now see the pay as guest button and you can complete your purchase!