PayPal integration from Braintree sandbox error: PAYPAL_SANDBOX_ACCOUNT_NOT_LINKED

I finally turn out open another Braintree sandbox account solve this problem. It is weird however I cannot solve by anything else.

_{Full disclosure: I work at Braintree. If you have any further questions, feel free to contact support.}

There are two sandbox accounts that you need to link together: your Braintree sandbox, and your PayPal sandbox.

Double check that you have followed the instructions in Braintree's documentation to link your PayPal sandbox account to your Braintree sandbox account within the Control Panel.

If you continue to see this error, please contact Braintree Support for assistance.