As mentioned to this thread :
Paypal changed : the sandbox now requires TLS 1.2 for all requests.
Miniu solution to change the core of wordpress /
curl_setopt ( $handle, CURLOPT_SSLVERSION, 6 );
somewhere on line 131 in wp-includes/class-wp-http-curl.php
seems to be a solution ... but it doesn't work to my configuration ... I ve upgraded php to 7.0 version ... but my version of curl is still: 7.21.0 .. and it seems to be not enough ...
so what could be a correct solution for my case ?