If your Shopify admin shows healthy stock but shoppers see "sold out", the cause is almost always the same thing, and it is not something you did wrong.
Arbyn now checks for this on your Catalog page and tells you which products are affected.
What is happening
Shopify will only let a location fulfil an online order if that location has shipping rates set up. A location with no shipping rates cannot sell, no matter how much stock sits there.
So if all of your stock is at one location, and that location is not part of any of your delivery profiles, Shopify treats every one of those products as unavailable. Your admin still shows the units, because the units are really there. The storefront shows sold out, because nothing can be shipped.
If your inventory policy is set to deny (which is the default), Shopify then hides the buy button entirely.
Why this usually happens with a fulfilment app
Apps like Trendsi, Printful, Printify, ShipBob and most dropshipping apps create their own location in your store and hold your stock there. That part is normal and correct.
The step that is easy to miss is adding that location to your delivery profile. Nothing in Shopify prompts you to do it, and the app usually does not mention it either.
You also cannot work around it by moving the stock. Shopify does not allow an item to sit at both a fulfilment app's location and one of your own at the same time, so adding the location to your delivery profile is the way through.
How to fix it
In your Shopify admin, go to Settings, then Shipping and delivery.
Open the delivery profile your products use. For most stores this is the General profile.
Find the section listing the locations that ship from this profile.
Add the location holding your stock, for example your Trendsi or Printful location.
Make sure that location has shipping rates for the places you sell to.
Your products should become available to shoppers shortly after. Shopify can take a few minutes to catch up.
How to check it worked
Open your Catalog page in Arbyn. The Not sellable count should drop to zero. You can also open any affected product on your live storefront and confirm the buy button is back.
The Products not sellable email
Arbyn emails you when it finds products that cannot be bought, so you are not relying on noticing it yourself. You can turn this off under Settings, then Notifications, where it is listed as Products not sellable.
It does not repeat while the problem is unfixed. An alert that arrives every day about the same thing stops being read, and this is one you need to read.
What Arbyn does about it
Arbyn flags affected products on your Catalog page, with the reason and the fix. The agent itself already tells shoppers the truth about availability, so it will never claim something is in stock when they cannot buy it.
If a product cannot be sold, Arbyn treats that as a problem worth showing you rather than a normal state.