TCGPlayer discontinued support for their API some time ago and there is no way to directly interact with your TCGPlayer account. However, one of the default features on TCGPlayer is the ability to export your inventory as csv data. TCGP Kit relies on this exported csv data in order for us to analyze, display, and edit your inventory so that it can be updated on your TCGPlayer account.
In order to export your TCGPlayer Inventory as a csv, you will first need to sign in to your seller dashboard.
From the menu at the top of your dashboard, click on the Pricing tab.
Once on the Pricing page, click on the Export From Live button to begin your download.
You should now have a csv file for your full TCGPlayer inventory. Go to the next doc to learn how to upload your inventory to TCGP Kit.