Stock that Amazon ships keeps its own count
We always send your figure out to Amazon. What comes back is the part that differs.
We send your count to Amazon whichever way an item is fulfilled, so a sale at the Lightspeed till lowers what Amazon shows either way. The direction that changes is the one coming back. For items you pick and post yourself, we take Amazon’s changes and carry them through to Lightspeed. For anything Amazon holds and ships, we leave the count alone on purpose.
That is a decision rather than an unfinished feature. Amazon owns what is sitting in its own warehouses and knows those shelves better than we do, so writing our number over theirs would mean guessing at receipts, damages and returns that never pass through your shop. Leaving Amazon authoritative over its own stock is the honest option, and it means the goods on your Lightspeed shelf are what this pair keeps in step.
The other thing to settle first is SKU length. Amazon truncates anything over 20 characters, the tightest limit of any channel we support, while Lightspeed takes 64. Twenty goes fast if you build codes out of words, and a truncated SKU stops matching the item it came from without raising an error, so the count simply stops moving. Shorten the pattern once, before you connect.