Hello Robostuy,
It sounds as though you have two different Apple ID's, and are attempting to reinstall an application that was previously purchased. When attempting to reinstall Minecraft have you verified that you're signed in to the correct Apple ID, or tried signing in to the alternate Apple ID to complete the installation? The reason the Apple ID being used is important is because if you're signed in to the wrong account you would be asked to purchase the app. Also, are you following the steps outlined in the article below to complete the reinstall? If not, that article can help with downloading previous purchases.
Redownload apps and games from Apple
Have a great day!