There are a couple of reasons why you might not be able to remove your credit card, bank account, or PayPal payment method:
Active paid subscription: If you have an active paid subscription with Rebrandly, downgrade to the Free plan before removing your payment method. See How do I change or cancel my Rebrandly subscription?
Auto-renewing domains: If you have a branded domain with auto-renewal enabled, turn off auto-renewal for your domains before removing your payment method. See How do I turn off auto-renew for my purchased domain?
Deleting a payment method is a permanent action and can't be undone.