Mulitsite Installations?

The free version can be used on multisites: Their limited features has no effects on this.
With the PRO-Version you can store Templates in the database for using it on multiple pages / blogentries. As these Templates are stored site by site multisite Management comes into the game. PRO-Versions prior to 2.0.9 do not support multisite. Versions after 2.0.9 are multisite ready.

Thanks to Rod from Canada and Layth from Australia!

Version 3.3.8 (Jun 18 2017): CURL-POST and Twig 2.4.3 possible

New:
Shortcode "method=curlpost" let's you use another method of http-connect: Now you can do POST via the Wordpress-build-in-Post (default), raw-PHP-post ("method=rawpost") and now new via Curl-POST (same with GET via Wordpress-build-in, raw-PHP-get and Curl-Get). Adding payload to the POST is done as with the other POST-requests via "postpayload" or "postbody", depending what the API requires.
New:
Shortcode "parser=twig243" (instead of "parser=twig" which invokes twig 1.X) let's you use twig Version 2.4.3, which is the latest twig-version. The difference between twig 1.X and 2.4.3 is not that much. If you're ok with twig 1.X you do not have to switch to 2.4.3.
Plugin is Ok with Wordpress 4.8
Minor Bugfixes:
If the "settings-pages" of the plugin-options was never saved, the default settings aren't in action. So templates with nested shortcodes did work only after saving this pages once.

Version 3.3.7 (Apr 1 2017):
New Shortcode-Parameter urlencodepostpayload, Bugfixes

New Shortcode-Parameter urlencodepostpayload:
When using POST for API-requests the payload (=parameters) might or not might be urlencoded. Default is encoding. By adding "urlencodepostpayload=no" to the shortcode no encoding is done. Some APIs require this.
Bugfixes:
"pathparam" was required to use "fileext" when building dynamic API-URLs. Now "fileext" can be used without "pathparam".
Bugfixes:
Extended debug-messages when using debugmode in shortcode. Fixing notice-errors when sorting JSON.