Credit (Visa, MasterCard, American Express, Discover) Visa or MasterCard debit cards PayPal Vudu or FandangoNow gift cards Walmart branded gift cards are no longer accepted.
On 12/31/2020, payments using credit cards from Walmart.com accounts will no longer be supported. Customers using Walmart accounts to login can add a payment method directly on vudu.com.
Please note your debit card limits or overdraft policy before adding it as a payment method, Vudu is not responsible for any incurred fees. Watching free movies does not require a payment method on file.
If the above is all met, then maybe try verifying that your Roku device is indeed linked to the card (as form of payment method) in your online Roku account. (https://my.roku.com/account).
Alternatively, you could go to the Vudu website, create a username and then pay directly at website. Then login to Vudo on your Roku device and see if you can watch the movie. There exists the possibility may be just experiencing an issue with the Roku payment processor currently.