Keeping an expansion store in step with your main catalogue
An expansion store sells the same products in another market: another currency, another language sometimes, usually a shorter range and its own stock. The catalogue is the same catalogue, which is exactly why keeping it identical by hand stops working around the second month.
Copy the product, not the pricing
Price is the field you almost never want copied between markets: your European store does not sell at the same number as your American one, and a sync that overwrites it every hour undoes the pricing work somebody did on purpose.
StoreTwin keeps price off unless you turn it on for that connection. Everything else - title, description, status, tags, options, your metafields, variants with SKU, barcode and weight - travels normally.
A shorter range is normal
Expansion stores rarely sell the whole catalogue: licensing, shipping restrictions and seasonality all cut it down. That is a first-class case, not a workaround.
Any StoreTwin connection can sync either the whole matched catalogue or only the products you pick, and whole collections or tags can be added at once. The products you did not pick are still audited: their differences appear in the report marked as reported only, so you can watch a product without copying it.
Stock is per location, always
If the expansion store ships from the same warehouse, send that location's stock and let the other store show it. If it holds its own stock, do not sync inventory at all and sync only product data.
The mapping is explicit in StoreTwin: the locations you tick in the sending store are added up and compared with one location in the receiving store. Leaving the selection empty means every location, which is the right answer for a single warehouse.
Translations and local edits
If your expansion store has translated descriptions, one-way sync will overwrite them with the source text - it is doing what you told it. Two workable answers: keep translations in Shopify's own translation layer rather than in the product body, or sync only the products whose text is shared and leave the translated ones out of the selection.
Proving it stayed right
The reason to care about audits in this setup is that nobody watches an expansion store as closely as the main one. A product that stopped syncing there in March is found in June, by a customer.
StoreTwin compares the two catalogues every night and emails a weekly summary, so the answer to "is the other store still correct" is a list rather than a hope. How the audit works ยท Setting up two stores