Step 1:

From the invoice sent via email, click the “view and pay invoice” button.

Step 2:

In the top left corner, hit the “Pay $” button.

Step 3:

*Important Part. Do not click “log in”. Instead, click the button below: “pay with credit or debit card”.

Step 4:

You will now be on the “Guest Checkout” page where you can pay with a credit or debit card without having a PayPal account.