Ted here from Shopify, thanks for posting your query!
Is this in regards to a subscription payment? If so, could you tell me the type of payment method you are entering? Is it, for example, a Visa/Mastercard or a credit/debit card? If you're trying to use a debit card payment method, this isn't normally accepted as we can only accept credit cards for subscription payments. That said though, have you tried using Paypal instead? Paypal can be selected in the Settings > Billing > Add payment method > Payment method type as shown here for example.
If you're referencing a different area in the admin or storefront, please let me know!