Costco sent out notice to members that after November 15, 2023, the online Costco.com will no longer accept Discover cards. As before, Costco clubs in-store only accept Visa cards. At Costco.com they previously accepted Visa, Mastercard, and Discover; going forward, only Visa and Mastercard will be options for online payment. You can see the full list of accepted payments at this Costco link.
Discover sometimes has Wholesale Clubs as a category. Costco would no longer be an option for that.
Hat tip to DDG
Source: doctorofcredit.com