The "Run now" feature on Synchronization is handy if you don't want to wait until the next execution date.
However, due to the APIs Quota/Rate limit of requests per second and many other parameters, we have to limit the usage of this feature to our paid offers only and for some synchronizations at a time.
It will not be possible to execute a Sync immediately if there's already a synchronization running to the destination music service.
YouTube and YouTube Music on Soundiiz are counting for the same service.
Thank you for your understanding.