Subscription Bug

We noticed one issue. I initially subscribed to a €1.00 plan and then upgraded to a €1.10 plan (a €0.10 difference). I expected to be charged only the prorated difference, but instead I was charged €1.00 again and €0.90 was added to my customer wallet.

Could you clarify why this happens, and whether it’s possible to charge only the additional amount so the upgrade is easier for customers to understand?