asp.net - Paypal Test API Link could not open secure channel -

the test api link not working in program.

please check following screen shot.

when type, test api url ( https://api-3t.sandbox.paypal.com/nvp ) value in browser address bar, return failure value , error message, know why happen not pass credential values , other mandatory fields.

according logic, when debug link (test api link) in program without credentials values, leading me exception instead of returns failure.

so try live api ( https://api-3t.paypal.com/nvp ) url whether make sure program errors or not, live api link give me failure result.

and test link still working in program last 2 days ago.

i using .net framework 4.5.

please tell me possible reasons why getting error.

thank suggestion.

that's because of endpoints updated use tls1.2, therefore should using securityprotocoltype.tls12 before nvpapicaller call. i.e

system.net.servicepointmanager.securityprotocol = securityprotocoltype.tls12; nvpapicaller ppcaller = new nvpapicaller(); 

....

more info on tls updates: https://www.paypal-knowledge.com/infocenter/index?page=content&id=faq1914&expand=true&locale=en_us