This page is organised by symptom. Find the thing that is happening to you, read the cause, apply the fix. Almost every problem merchants hit with this app has one of a small number of causes, and the great majority are a gate that has not been satisfied rather than a fault.
If your issue is Amazon rejecting or complaining about a specific listing, that has its own article: Fixing listing issues.
What you see: "This app must be opened from your Shopify admin (Apps, Amazon Price Sync)." or "Could not authenticate with Shopify. Please reload the app from your Shopify admin."
Cause. The app is an embedded Shopify app. It only works inside your Shopify admin, where Shopify hands it a session token that proves who you are. Opening it from a bookmarked URL, a saved tab, a link in an email, or a browser window where your Shopify session has expired gives it no way to authenticate you.
Fix. Go to your Shopify admin, open Apps, and launch Amazon Seller Sync from there. If you were already inside the admin and it still fails, your session has simply gone stale. Reload the page. If it persists, log out of Shopify and back in.
Tip
Do not bookmark the app's URL directly. Bookmark your Shopify admin's Apps page instead.
What you see: "Missing: {scopes}. Reopen the app to re-authorize." The Settings > Automation tab also warns you when scopes are missing.
Cause. Scopes are the permissions Shopify grants the app: to read products, to write inventory, and so on. Occasionally the app needs a permission it was not granted at install, typically because you have upgraded, or because you are turning on a feature such as Fulfilment by Amazon that needs permissions the app deliberately does not ask for until you use it.
Fix. Close the app and open it again from your Shopify Apps menu. Shopify will show you the permission prompt. Approve it. The app cannot request permissions while it is already running, which is why reopening is the fix.
If you see "Permissions were declined. They're needed to manage Amazon fulfilment and tracking.", you clicked away from the MCF permission prompt. Reopen and accept it. Without those permissions the app cannot fulfil your orders through Amazon.
Cause. No Amazon account is connected. There is nothing to sync from, so the button is disabled rather than failing.
Fix. Go to Settings > Amazon account and connect an Amazon Seller Central account. If an account is listed but the button is still disabled, its authorisation has likely lapsed. Use Reconnect. See Connecting Amazon.
This is the most common report, and it is almost always one of three gates. Walk them in order.
Gate 1: target marketplaces. You have to tell the app where to publish. If you have not, pushing is blocked outright with "Select at least one marketplace to publish to before pushing." Open Marketplaces to publish to on the Product Sync screen and pick at least one.
You may also see "No connected Amazon marketplaces found. Connect an Amazon account first." or "Connect at least one Amazon Seller Central account before pushing listings." Those mean the connection itself is missing, so fix that first.
Gate 2: Amazon product type. Every listing must declare a product type, and there is no default. If the app cannot resolve one for a product, the product shows Needs type and nothing is sent. The message is: "Set an Amazon product type for this category (per marketplace) before pushing."
Use Set type. The app suggests a type based on the Shopify category and you confirm or change it. The type applies to every product in that Shopify category, per marketplace, so this is a chore you do once per category, not once per product. See Amazon product types.
Gate 3: required Shopify fields. A product cannot even be selected for pushing until its Shopify Brand (vendor) and Description are filled in. On the product detail page you will find AI, Apply and Push all disabled until they are. These are not app fields. Set them in Shopify, on the product, then come back. See Required Shopify fields.
If all three gates are green and you still see nothing, check your plan. Product Sync is a paid feature, from Growth upwards. On Free you can map and sync prices but you cannot publish listings.
Cause. Usually the Choose your marketplaces step. It completes only when you have explicitly saved a market mapping. A marketplace that the app inferred from your connected Amazon account does not count, even though the app is clearly using it.
Fix. Go to Settings > Markets, choose your default (home) marketplace, and save. The step ticks.
The other steps are more literal: connect an account, acknowledge the conflicting apps check, map at least one product, and publish at least one product. See The setup checklist.
Work through these in order.
The variant is not mapped. Price sync only touches variants that have an ASIN attached. On the Product Mapping screen, filter to Needs mapping and see if your product is sitting there. Map it, or run Auto-match one-to-one if it has a barcode.
The sync interval has not elapsed. Free syncs every 24 hours. Paid plans sync every 6 hours. If you mapped a product ten minutes ago, its price simply has not been fetched yet. Click Sync now on the Dashboard to force it.
Amazon has no offer. If nobody is currently selling that ASIN as New, there is no lowest offer for the app to fetch, so there is no price to write. The product will show as having no price and this is correct, not a bug.
The barcode is wrong. Auto-match matches on barcode alone. A wrong barcode maps you to the wrong ASIN, and you get a real price for the wrong product. If a price looks bizarre, check what ASIN the variant is mapped to. See Auto-match.
The product was never published through Product Sync. Inventory Sync pushes stock for listings the app owns. A product merely mapped for price sync shows in the read-only Price-mapped products card and is never pushed.
The SKU is FBA, not FBM. The app detects fulfilment type per SKU. If the SKU appears in Amazon's FBA inventory, Amazon holds the stock and the app treats it as read-only. It will show you Amazon's availability but it will never write to it. Only merchant-fulfilled (FBM) SKUs are pushed. This is correct behaviour, not a limitation.
Inventory Sync is a paid feature. It is available from Growth upwards. On Free you will not have it.
If none of those apply, note that FBM push is not on a schedule. It fires within seconds of a Shopify stock change. If your stock has not changed recently there is nothing to push. Force it with Sync all FBM inventory. See How FBM stock reaches Amazon.
Five causes, in rough order of likelihood.
It is not enabled. Enable automatic repricing is off by default. Turning it on saves immediately.
You already hold the Buy Box. This is the big one, and it is by design, not a fault. If you are already winning the Buy Box, lowering your price gains you nothing and costs you margin, so the repricer holds. The last-run summary counts these as "held (winning)". A run that reports lots of holds and no changes is a run that did exactly what it should.
The product is mapped only, not published. Only products published through Product Sync are repriced. Products mapped on the Product Mapping page are never repriced, because the app does not own those listings.
The interval has not elapsed. The repricer runs on its own Run every setting, from 1 to 168 hours, independently of your price sync interval. Use Reprice now if you do not want to wait.
The price is clamped at the floor. The repricer will never go below your floor, which defaults to 85% of your Shopify price. If the competition is below your floor, the repricer stops at the floor and counts the listing as having hit it. It will not chase. That is the safety net working. See Price floor and ceiling.
Cause. The button hides itself entirely when no URL resolves for that product in the shopper's market. It is designed to disappear rather than render a dead button.
Fix. Check, in order: is the variant mapped to an ASIN at all; has a price sync run since you mapped it, since the Amazon URL is written by the sync; and is the shopper's market mapped to an Amazon marketplace. On the Free plan you get only the default marketplace, so a shopper in an unmapped market falls back to your home marketplace link.
You can also set an override URL, either store-wide or per product, under Buy on Amazon. See Buy on Amazon button.
Cause. Buy Box history is recorded on each price sync. It is not fetched retrospectively from Amazon, because Amazon does not hand out that history.
Fix. Wait. The report fills in as syncs happen. On Free, at one sync a day, a 30-day report takes 30 days to fill. On a paid plan at 6 hours you build a useful picture within a few days. Nothing is broken; the data simply has to accumulate. See Analytics.
Symptom. Prices or stock levels on Amazon flap back and forth, changing to one value and then to another shortly afterwards.
Cause. Two apps are managing the same Amazon listings and are overwriting each other. The app checks for this on setup and detects the common ones, including Codisto, CedCommerce, ByteStand, Sellbrite, SellerCloud, Reputon and Shopify's own Amazon sales channel.
Fix. Decide which app owns which function and turn the other one off for that function. The Is another app managing your Amazon? modal lets you tick which functions another app handles (Pricing / repricing, Inventory & stock sync, Creating / editing listings, Fulfilment (FBA / MCF)), and after you have disabled them in the other app you click I've disabled these, recheck.
The check is a warning, not a hard block, so you can override it and continue. Be aware of what you are choosing if you do. See Conflicting apps.
If your problem is not here, the two most useful things to gather before asking for help are the exact error text the app showed you, and which plan you are on. A large share of "it does not work" reports resolve to a paid feature being used on the Free plan.