The most common cause is Modules allowed Online: on a brand-new pickup location every module toggle is off, so any cart item is refused with Unfortunately we cannot process your item "<module>" using the Pickup method. Open the location and tick the modules (Meal Packs, Weekly Subscriptions, À la Carte, Catering…).

Other checks: the location must be Is Active? (inactive locations are excluded from the checkout's pickup list), the delivery date's weekday must be ticked under Meal Prep Pickup Availability (This pickup don't allow this day), Allow Pickups must be Yes in Client Config, and if the customer is under a Corporate/Parent Membership Restriction the location must be in their allowed list.