To test paypal payments you need to:
Create developer account
Add seller and buyer in developer sandbox
Add seller and buyer¶
Go to Dashboard->Sand box->Accounts. Create business (seller) and personal (buyer) accounts. It’s recommended to don’t use non-ascii symbols in account information (address, name etc.)
Add some money to buyer (type amount in according field).
Go to http://sandbox.paypal.com and login as seller. May be you will be forced to apply unconfirmed ssl certificate.
Install payment_paypal module
Go to Settings->Payments->Payments->Paypal.
Enter here Paypal Email ID - it is seller account.
Open web shop. Buy some goods and pay with paypal. When you will be redirected on paypal page use buyer login and password.