If a customer has paid $25 for a plan with 4,000 credits and still have 2,000 credits remaining at the end of your billing period, it makes more business sense to customers that they don't lose the 2000 credits ($12.5)
Instead you can give an additional 1 to 3 month window for customers to utilise their unused credits before wiping them out. You can step the customer down to free plan but allow them access to use the credits they have already paid for
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