Your plan tier in Easync is determined by how many listings you have, so pick the plan that matches your listing count (e.g. 2K, 5K, 10K).
Once you connect your eBay store, Easync automatically syncs your existing eBay listings, and that synced count is what the required plan is based on — which is why the listings number (and the plan it forces) may look higher than you expect even if you haven't uploaded anything through Easync yourself.
To change plans, go to Account → Subscription and select the plan you want; if the upgrade is mid-cycle it's prorated, and the upgrade invoice must be paid or the store can get blocked.
If you can't select the tier you expect or the count looks wrong, send support a screenshot and they'll check it with the tech team.