TikTok only allow the use of their promote button for posts using sounds from their Commercial Library or an 'original sound'.

This is a good thing, as it stops other users using your music to promote their business, product or service without your permission.

As they currently don't support artist verification, it isn't possible for artists or Record Union to confirm that they are the artist behind certain tracks and so should be viewed as original. This means that music you have delivered to TikTok via Record Union cannot be used in posts that you wish to promote.