Hi Jordy
Adding to this thread as I am having a similar issue but believe I know the cause (just not sure how to fix it).
For some reason when I set up my site, I did so in a subdirectory of the public_html folder. So when I went to Google Analytics and created the app for the OAuth ID, your plugin told me to use https://mysite.com/folder for the authorized Javascript origin but Google didn’t like that and wouldn’t accept a subfolder. If I use https://mysite.com, Analytics data is empty in the dashboard.
This may be a site-specific/Google-specific weird interplay that can’t be solved. Really love how light your plugin is compared to the annoying one I deleted…
If you have any thoughts, I would love to hear them.
Thanks for creating this!