Hey @Pinhead71. I hope you have solved your issue. If it still persist, try checking your webgl build if it contains a html file.
If it does, make sure it is named "index.html" specifically.
Then make sure your build is compressed as a ".zip" file before uploading.
These are the issues I faced before, hope it helps.
Just noticed your message in the discord. Looks like its working for you already. Good luck!