Samn Dammett commented
My suggestion is this (developers don’t like it, but some are cool with it). Whenever you see an app that comes in two or more versions (a free AND a Pro paid version) do NOT,
DO NOT upgrade using an in-app purchase. Download the free version just to test drive the app, and if you like it enough and want the full version, ALWAYS delete the free version and buy the Pro version separately. If you want to tranfer files between free and Pro, purchase the Pro separately, do the transfer, then delete the free version. But DO NOT PURCHASE AN IN-APP UPGRADE.
The reason is simple. You are allowed to share purchased apps (like Pro) on a family plan with family and friends, but you are NOT allowed to share in-app purchases. So if you buy Pro on its own, your family can download the app for free. But if you purchase a in-app upgrade, your family members have to but their own copy of the app. If you have brothers or sisters, spouses, parents, children, or friends who could use the app, it is better for them to share in a family plan.
付了两遍钱的同学们可以在 App Store 申请退款。一般情况下都是会退的，理由用中文写就可以了。