unable to communicate with the paypal gateway in magento 2
I find the solution, It was about Outgoing Connections which web hosting company was blocking it, after talking with support, they allowed Outgoing connections to paypal website. now its working.
https://community.magento.com/t5/Payments-PayPal/Unable-to-communicate-with-the-PayPal-gateway/m-p/19910#M289