1. Why aren't customers directed to Paypal to finish the payment?
URL forwarding and Frame for your own domain are not allowed by Paypal, because it is regarded as insecure. You may need to set your own domain via the standard steps.
2. My paypal orders don't show up
PayPal sometimes experiences delays in their IPN (Instant Payment Notification) service which is the mechanism used to tell Miiduu about completed orders. Delays can range from a few minutes to several hours. If the orders still don't show up, you should deliver products based on the payment record in your Paypal account. You may find your missing orders under menu: Sales->Order->Missing order.
IPNs are only part of the Website Payments Standard package. Website Payments Pro does not have this issue and all orders should show up immediately.
3. Currency Issue
If your default currency is not USD (as default currency in Paypal), you need to confirm that your currency is accepted by Paypal. What's more, make sure the currency code in your dashboard ("Settings"->"Localisation"->"Currencies"->"Code") is in accordance with Paypal.
4.This transaction cannot be processed due to an invalid merchant configuration.
Please complete the following checklist:
1) Make sure you've signed up with PayPal for PayPal Website Payments Pro. This is a service provided on top of the standard PayPal package and costs approximately 30$ USD a month.
2) Make sure that you have accepted the "PayPal Payments Pro" agreement in your PayPal account after you have been approved by PayPal for PayPal Payments Pro.
If you still have the same error then:
3)Log into your PayPal account. Go to “Profile” then "My selling tools” then "API access”, "View API Signature”. Removed the API Signature and recreate it. Go back to your Miiduu account and input the new API information.
5.The seller accepts encrypted website payments only. You cannot pay the seller through un-encrypted buttons. Please contact your seller for more details.
You need to turn off the PayPal encrypted website payments feature
1)Log in to your PayPal account.
3)From the Selling Preferences column, click Website Payment Preferences.
4)In the Encrypted Website Payments section, select Off.