Issues with Syncing a Score with a Youtube Video

Hello,

I am currently trying to sync a score uploaded to the website with a youtube video I created and have attempted various ways to do so. The score in question is this one: https://musescore.com/user/6620691/scores/8043258

Using the "Manage audio sources" feature, I have linked the score to the video in question and both attempted to:

1) set the transitions from bar to bar myself with the M key;
2) automatically sync the video with the score using the "Load Score Markers" feature.

While I couldn't find out how to sync the various transitions manually with the audio - the piece repeats in the latter half and then progresses into a conclusion, which I couldn't visualise in the movements from bar to bar -, the "Load Score Markers" feature seems to do the job perfectly: all the transitions now line up precisely with the audio of the video.

The problem is this: the audio used when playing the score is still unchanged and that of the basic musescore soundfonts - synced perfectly or not, the audio of the video is just not being played.

I don't understand this and would be very grateful for some help. The screenshot below shows what the site is currently presenting to me - I don't see any obvious issue.

Thank you for your time.