Login to your Supliful account.
On the top, click Stores.
On the Stores page, under Add new store click on the WooCommerce tab:
In the pop-u window enter WooCommere store details and click Connect.
Make sure, your WooCommerce store name does not have /Shop at the end/
Like this -
wordpresshostname/shop. This does not allow REST API connection.
You will be taken to the WooCommerce connection page. Make sure you are logged in as the correct user and click Approve:
Your newly connected WooCommerce store will immediately appear on your Supiful Stores page and you can start publishing products right away.