It appears that the newest sqlsrv driver only supports PHP 7.0 and not 7.1. Maybe you should add PHP 7.0 to ExeOutput. After you get the curl problem fixed
I found the sqlsrv driver for PHP 7.1 here: https://github.com/Microsoft/msphpsql/releases
It would have been surprising that there is no driver for V7.1. Thanks for the link!
Except that I couldn't find a link to it on the Microsoft web site.