Distributing your app with AltStore PAL is similar to what you may be used to when submitting to the Apple App Store. You will still submit apps through App Store Connect using your paid Apple Developer account, so make sure you are set up with one before proceeding. The only major difference is that your apps will only be available in the EU.
The Alternative EU Terms Addendum is an additional agreement you must make with Apple in order to distribute your apps outside the App Store.
Before you can submit your apps to AltStore PAL, you must prepare your developer account for distribution with alternative marketplaces
Email your Developer ID to apps@altstore.io. You can find your Developer ID in App Store Connect by selecting "Edit Profile" in the top right.
You will receive a response with a security token. In App Store Connect, go to Users and Access -> Integrations -> Marketplace, click '+' and input the token.