How can we improve WHMCS?

We have some products (as Microsoft 365 accounts) that can be billed monthly but with an annual contract, now we can only offer monthly billing with monthly contract or annual billing with annual contract. It would be great to have the possibility to have an annual contract with monthly billing. On that option, WHMCS will bill monthly the service BUT it cannot be cancelled until the end of the contract. In case of optional configurations or upgrades of product, you can upgrade or add items to this service, but you cannot downgrade until the end of the contract.