Unfortunately, you will be charged the full amount for the new subscription tier. Apple's App Store policies do not allow for prorated upgrades for annual subscriptions. This means that you will be charged the full price of the new tier even though you have already paid for a portion of your current subscription.
Here is a more detailed explanation of Apple's App Store policies regarding annual subscriptions:
- Annual subscriptions are billed upfront and not prorated. This means that you will be charged the full price of the subscription when you first sign up, even if the subscription is not active until a later date.
- You cannot cancel an annual subscription and then re-subscribe at a higher tier to get a prorated upgrade.This is because Apple's App Store policies do not allow for prorated upgrades for annual subscriptions.
The only way to upgrade your annual subscription to a higher tier is to contact Apple Support and request a refund for the remaining balance of your current subscription. Once you have received a refund, you can then re-subscribe to the new tier.
I understand that this is not the answer you were hoping for, but I hope this explanation helps you understand the situation.