I'm using Paypal Sandbox Account. I'm facing below issue
[2017-03-15 03:32:20] main.CRITICAL: Exception message: PayPal gateway has rejected request. Payment has already been made for this InvoiceID (#10412: Duplicate invoice).
Trace: #0 D:\wamp\www\magento\vendor\magento\framework\ObjectManager\Factory\Dynamic\Developer.php(89): Magento\Framework\ObjectManager\Factory\AbstractFactory->createObject('Magento\\Framewo...', Array)
#1 D:\wamp\www\magento\vendor\magento\framework\ObjectManager\ObjectManager.php(57): Magento\Framework\ObjectManager\Factory\Dynamic\Developer->create('Magento\\Framewo...', Array)
#2 D:\wamp\www\magento\var\generation\Magento\Framework\Exception\LocalizedExceptionFactory.php(43): Magento\Framework\ObjectManager\ObjectManager->create('\\Magento\\Framew...', Array)
Best Answer
By default Paypal does not allow you to put through the same invoice number twice. This can happen when you use the same credentials across multiple different Magento sites (even across a local environment and your staging environment)
You can change this behaviour in Paypal under Your Profile > Selling Tools > Block payments and then change the setting for Block accidental Payments to
"No, allow multiple payments per invoice ID"For me the direct link to the relevant settings is https://www.paypal.com/cgi-bin/customerprofileweb?cmd=_profile-pref