Hi Daniel,
I'm new to Construct 3 and I have a site hosted with you so I gave this a shot in one of the games I'm editing. However I have not been able to get it to post high scores. To be perfectly honest, I really don't have much of an idea of what I'm doing, but I followed the instructions as best I could with no luck.
I wasn't sure if I needed to but I used the ValerypopoffJS plugin for Construct and called the "myarcade_submit_score( score );" function using it. I also imported myarcadebridge.js into Construct 3 under "Files". When I imported the game using MyArcadePlugin Pro I checked the box that this game was able to submit scores to a Leaderboard.
The function call is directly underneath where I submit high scores to Google Play, which is working in the app version.
Here are some screenshots of my Construct 3 project if it helps ...
Any help would be much appreciated!