Shuttle stopped this product because it has more than 400 variants in Shopify. It did not send it to Etsy.
Why it happens
Shuttle stops a product with more than 400 variants when you:
transfer it from Shopify to Etsy, or
update it with Recreate Etsy inventory ticked (Recreate product inventory in a bulk update). This rebuilds all of its variations on Etsy.
It does not matter if the variants have the same or different SKUs, prices or quantities. Every variant of the Shopify product counts, so open the product in Shopify and check how many variants it has.
How to fix it
In Shopify, open the product and count its variants.
Bring it down to 400 variants or fewer. You can delete variants you no longer sell, or split the product into two or more Shopify products with 400 variants or fewer each.
In Shuttle, open Products, choose the Shopify → Etsy tab and find the product.
If the product is not on Etsy yet, click Transfer to Etsy.
If the product is already on Etsy and you were rebuilding its variations, click Update in Etsy. In the Update product window, tick Recreate Etsy inventory, which also ticks SKU, Price and Quantity, and click Update Etsy product.
Update a product on Etsy without changing its variants
If the product is already on Etsy and you do not want to change its variant count, you can still update parts of it. Open Products, choose the Shopify → Etsy tab, click Update in Etsy next to the product and choose what to update in the Update product window:
To update only the title, description, tags or images, leave Select all fields unticked, untick Quantity, and make sure SKU and Price are unticked too. Quantity is ticked when the window opens, and Select all fields ticks every field, including SKU, Price and Quantity, so the variant limit would apply again. The variant count does not matter for these updates. In a bulk update, untick Overwrite all fields instead.
To update SKU, Price or Quantity, leave Recreate Etsy inventory unticked. This only works when every variant has the same price and the same SKU (or no SKU), and the product has 1,000 variants or fewer. If not, the update stops with a different variant limit message.
Still seeing it?
If the product has 400 variants or fewer in Shopify and you still see this error, contact support. Tell us the product name so we can look into it.