It seems to be impossible to sign-up for the Chase Instacart credit card right now. The link, www.TheInstacartMastercard.com, leads directly to the Instacart main page without even mentioning the card at all.
Chase doesn't have the sign-up for it either at their website, creditcards.chase.com/instacart.You can only sign-in at Chase, if you already have the card.
Did they close the card for new customers?