After you Confirm your order on Alan's Sales, you are taken to a PayPal screen such as the one below or similar. If you do not have a PayPal account, on lower right click on, "Don't have a PayPal account?". Click here for more information on limits. 

If you are using your PayPal account just log in to PayPal in the appropriate box.

If you have a personal PayPal account and do not wish to use it, such as for a business purchase, your email address must not match your personal email address that you have registered with PayPal. PayPal will try and access your personal account. Possibly, you may need to return to Alan's Sales and in your account edit the email address and use an email address that PayPal does not have registered.  Return to PayPal again by Confirming your order once more.

PayPal limits: For those who do not want to register an account with PayPal, at the time of this writing, PayPal has a $2,000.00 use limit on which a particular credit card may be used. After the limit is reached the purchaser may either create an account with PayPal with that particular credit card or use a different credit card for their purchases, but there will also be a use limit of $2,000.00 on that card also. Time is not a factor with the use limit, only the dollar amount.