Your Shopify and SellSN products need to be synced. We know this can be annoying but this is a one time process.
https://dash.sellsn.io/settings, click Copy ID at the top right.
482304198249714c4f0add-cc18-4d5b-b47f-b143a6a29d9c
custom-script.js file.
custom-script.js file to your Shopify theme's Assets folder.
theme.liquid file and include the script with the following code, placed just before the closing </body> tag:
{{ 'custom-script.js' | asset_url | script_tag }}