Didn't work, but that did point me in the right direction. Embarrassingly enough it didn't occur to me that it could be my Pihole and after disabling it the widget loads successfully. Thank you for the help, and sorry for not using my head.
When I go to the premium checkout page under the "Choose a payment method" there is only one option and that is the "Payments by Braintree" option. Clicking this takes me to a page that tells me NexusMods is a customer and this verifies they are a customer. It doesn't seem to lead me to a payment portal. There are no other options. I've included a screenshot of the "Choose a payment method" portion of the page.