Follow this video if you just opened your account on ExportYourStore.
How to connect your Poshmark account to ExportYourStore
Download the ExportYourStore browser extension for the web-browser you are using.
Make sure you are logged in to your Poshmark account. If you already are, try opening Poshmark on another tab.
Once done, ExportYourStore will automatically detect your account and connect it to the service, then you'll be able to export & sync to Poshmark just like your other channels.