Just a quick note on my experience getting my Garmin device to sync with Spotify. I see from the Garmin Forum and Reddit that this seems to be a notoriously difficult challenge. On my home network (which uses Orbi Wifi routers broadcasting at both 2.4 and 5ghz), no matter what I did, my Forerunner 745 would not download my running playlist on Spotify. I tried everything with no success- bringing the device closer to the router, creating a dedicated 2.4ghz network on my router, and trying to reinstall Spotify on the watch and restart the device. At best, the device would download one song at a time before announcing that the sync failed (red circle with an error message).
Ultimately, what worked, was when I created a 2.4ghz hotspot on my Windows PC (connected to the internet via an ethernet cable to the router), and got the device to use this wireless network. The sync then worked flawlessly (and very quickly).
tl;dr: Creating a 2.4ghz exclusive hotspot and connecting my watch to that wifi network fixed my Spotify sync errors.