Problem
You cannot change a membership from monthly installments to annual after selling it.
Solution
Go to the customer's profile.
Find the membership that you want to change the billing frequency.
Edit the membership to review the details to confirm the current billing cycle. Since the system does not allow changing the billing cycle from monthly to annual for an already sold membership, you need to resell the membership.
Cancel the current membership.
Sell a new membership to the customer, selecting the annual billing option during the selling process.
Remember, when reselling the membership, be sure to select the correct billing option to avoid similar issues in the future.