I believe the problem is that your server is providing JSON files with the wrong MIME type. It's labelling them text/html instead of text/plain, or even better, application/json. See screenshot. Contact your web host for assistance.
Ah, I see now - you're uploading outside of the server root. Create an "album" folder below the "public_html" directory! That's the web root, anything outside of that is inaccessible through the web server.
Now had time to try this out and unfortunately it still does not work. I have tried a number of variations including putting in the URL of the album but no luck so far.
I think now is the time to give it up. I have spent hours trying t get this to work and really do not have the coding experience or the time to investigate further.
I can still use the idea of the collaborative album and then either use either an embed code or download the images from the collaborative album and then use another plugin to display them that I know works in the WP theme that I am using.
The possibility exists that the plugin will change over time and might work in future for me.
if have this tackled by adding the CORS stuff in the .htaccess files. Still nothing.
I managed to get an offline (localhost) webpagina to work but only by pointing to a local jquery.js and not the google one.
Edited by: gvmelle on 28-Apr-2018 19:09
Another thing: I managed to show a subfolder album with a name without spaces like "collages" but failed to show a subfolder with the name of "Het jaar 2018/Rondje Achterhoek 14 jan 2018" or "Het%20jaar%202018%2FRondje%20Achterhoek%2014%20jan%202018"