In order to use the built in Instagram widget on your store we first need to get some permission from Instagram to allow those images to be shown by means of an Access Token.
Click on the button below, this will bring up an Instagram prompt asking you to Authorize the Underground feed to access your Instagram photos.
We do not have any access to your account or images, this simply lets our app do it's thing and show those images on your store. You should then see a confirmation page with a long string of numbers displayed.
Thanks for completing those steps, here's your Access Token:
Copy this number and head over to the themes > customize theme section of your Shopify store. Select your Instagram feed section and paste this in to the field labelled: Instagram Access Token