What will happen with the credits if I cancel my subscription?
Subscription credits are valid as long as you have an active subscription. If you cancel you will be able to use them until the end of your billing period, later you will be downgraded to the free plan and unused credits will be invalidated.
For example, if you subscribe on March 15, and cancel on March 17, you can use the credits until April 15, as this would be your next billing date.
If you want to keep the credits for longer, without monthly (or yearly) payments, you can purchase Pay-as-you-go credits. They are valid within 2 years of purchasing and it's a one-time payment.