Before you map a single product, it helps to understand how Amazon organises selling accounts. Amazon is not one global shop. It is a set of regional groups of marketplaces, and your Seller Central account belongs to exactly one of those groups. Amazon Seller Sync mirrors that structure, which is why the app talks about accounts, regions and marketplaces as three separate things.
Region. Amazon splits the world into large selling regions. Amazon Seller Sync supports three of them: North America, Europe and Far East. A region is the level at which Amazon issues your selling credentials, so it is also the level at which the app connects.
Marketplace. A marketplace is a single country storefront inside a region, such as Amazon in Germany or Amazon in Canada. The app supports 21 marketplaces across the three regions. See the Marketplaces reference for the full list.
Account. Your Seller Central account sits inside one region and gives you access to the marketplaces you are authorised for within that region. One connection in Amazon Seller Sync represents one account in one region.
This is the point that catches most merchants out.
A Seller Central account covers one region only. If your account is a European account, it can reach Amazon in the UK, Germany, France and the other European marketplaces you have unlocked, but it cannot reach Amazon in the United States. The US sits in the North America region and needs a North America account, which Amazon treats as a separate account with separate credentials.
So if you want to sell in both the US and the UK, you need two Amazon accounts connected to Amazon Seller Sync: one for North America and one for Europe. Connecting your European account twice will not unlock the US, and there is nothing the app can do to bridge the gap, because the limit comes from Amazon rather than from us.
Within a region, the opposite is true. One European account can serve every European marketplace you are authorised for, with no second connection needed. Adding Germany, France and Italy alongside the UK is a matter of marketplace authorisation in Seller Central, not a matter of another app connection.
Note
If you are only ever going to sell in one region, one connected account is all you will ever need, and every plan including Free supports that.
Each Seller Central account has a seller ID, sometimes called a merchant token. Amazon Seller Sync stores one row per combination of region and seller ID. That pairing is what makes a connection unique.
The practical consequence is that the same seller ID connected in two different regions counts as two accounts, and two different seller IDs in the same region also count as two accounts. Both cases are supported, and both consume an account slot on your plan.
You do not tell Amazon Seller Sync which marketplaces you sell in. When you authorise the app in Seller Central, the app asks Amazon which marketplaces that account is actually authorised for and stores the answer. Everything downstream, including the marketplace list in Settings > Markets, the Marketplaces to publish to selector in Product Sync, and the FBA marketplaces list in Fulfilment by Amazon, is built from that discovered list.
If a marketplace you expect is missing from a dropdown, the cause is almost always that the account is not authorised for it in Seller Central yet. Add the marketplace on Amazon's side, then use Reconnect on the account in Settings > Amazon account so the app refreshes what it knows.
The number of Amazon accounts you can connect at once comes from your plan.
| Plan | Amazon accounts |
|---|---|
| Free | 1 |
| Growth | 1 |
| Growth + Markets | 2, plus extra account slots as a paid add-on |
| Full | Effectively unlimited |
If you try to connect one more account than your plan allows, the app shows "Account limit reached ({limit}). Upgrade or add an account slot." Nothing breaks and nothing is lost. You simply cannot add the connection until you free a slot or move up a plan. Connecting multiple Amazon accounts covers this in detail, including what happens if you later downgrade.
Once at least one account is connected, tell the app which Amazon marketplace is your home marketplace, and optionally map your Shopify markets to specific Amazon marketplaces. That is covered in Mapping Shopify markets to Amazon marketplaces. You can also review the whole connection flow in Getting started.