Note: We would be recommended using the Rest API integration method:
Go to AliDropship → Settings → Payments to enable PayPal as your payment gateway. Select Classic from the Integration method dropdown menu.
Add your PayPal email → click Save Changes.

Please make sure you have the correct settings on your PayPal account, as shown below.
Go to Seller tools, find Website preferences and click Update.

Website preferences:
Done! For any further questions, please get in touch with our Support Team: support@alidropship.com
If you have any issues with your PayPal account, please, contact PayPal Support.