The static file test fails? Then config of nginx/certs - I would think ...
What was the full screen ... did it have something like 'site can be reached via ... blah, blah, blah' or some additional info?
For Moodle ...
https://docs.moodle.org/36/en/Transitioning_to_HTTPS but that's higher version of Moodle than you are running. Instead, you will have to use a hidden tool for replace ...
Why? Moodle uses the wwwurl to build *all internal to moodle links* ... currently they are all http:// and need to be changed to https://
Another way to do this ... make a sql dump of database.
Edit the .sql dump with an editor that has search and replace ... nano has it ...
Search for 'http://yoursite/' ... include the protocol (http://) in front of the FQDN of site and also include the 'traling slash'.
Replace with https://yoursite/
You want to replace ONLY internal URL's ... not URL's that might have been used as links in courses.
Save the edited sql dump with a slightly different name ... moodle-edited-ssl.sql.
Create a new DB ... (newmoodlessl) import the moodle-edited-ssl.sql dump.
Change config.php file point to the new DB 'newmoodlessl').
Actually safer to copy the DB name line, then paste it back in ... comment out the original line // in front ... and the new line has 'newmoodlessl' + the https:// in site url.
Purge the caches.
Can do that manually ... in moodledata ... that's moodledata .. remove the contents of ... that's remove the contents of moodledata/cache/ It will rebuild as site is used.
Server logs ... error and maybe you have ssl_error might give a clue hint.
Plus ... if running something that has added protections ... centOS 6-7 for example has sELinux in enforcing mode. Your system ... dunno.
Suggest you PM me the URL this server and let me do some remote poking/probing.
'spirit of sharing', Ken