Patching an app
The download link on the official Lucky Patcher website frequently breaks and spams you with pop-ups in the browser. Use an adblocker - uBlock Origin for desktop browsers and AdGuard DNS for Android - if you plan to visit the website.
Alternatively, you can use a direct download link from the developer's website or the #resources channel on the unofficial Lucky Patcher Discord server (the former is sometimes down).
Set up Lucky Patcher
Read the important info about LP section.
Follow the tutorial on the official website. For patching inapp purchases, make sure to give LP the "Draw over other apps" or "Display pop-up windows" permission. This permission is needed because LP replaces the Google Play purchase popup window that normally shows when you try to purchase something in an app with its own popup containing some settings that can help in getting the item for free.
This special permission can be found in the app's settings. The app settings can be found by long pressing the app in your phone's app drawer. The location of this permission depends on your firmware.
Examples:
App info > scroll down to Advanced > Display over other apps
App info > Other permissions
Create the modified APK file
Follow these screenshots to create your modified APK file. Read any pop-ups you may come across and try to follow their advice, but don't worry too much about them.
First, open Lucky Patcher and tap the app you'd like to modify.
On this screen, tap the "APK with multi patch" option. The two most useful patches are the ad-free and IAP (InApp Purchase) patches.
Apply some patches.
If the patched app crashes or shows an error when you open it, try applying the Removes integrity check and signature verification and Fake a modified APK archive from the original patches as well. This helps sometimes.
Finally, install the modified APK file by tapping the "Go to file" button and then the "Uninstall and install" button.
Reinstall the app
When you reinstall (uninstall the original app and install the patched one) you will no longer be able to use Google features like Google Play sign-in in that app anymore. However, some patchable apps like Merge Dragons and City Island 5 allow signing in via Facebook, which usually works. However, if you have the Facebook app installed on your device you have to uninstall/disable it to be able to sign in to apps with Facebook.
Whenever APKs for Android are modified in any way, the APK must be signed before it can be installed. The signature of a Play Store app will always be different and cannot be spoofed. Android does not allow updating an app using an APK with a different signature. As a result, you will have to uninstall the unmodified app before installing the patched one. However, if you already patched an app with LP, and are patching over the patched version again, you can update it as the signatures will match.
Cleanup
You'll also be able to find the patched APK files in LP under the "Rebuild & Install" option in the menu. If you'd like to clean up some storage, remove these APK files manually. This menu only allows deleting one file at a time. You can clean up all of your patched APK files at once by opening the settings of Lucky Patcher, selecting "Change Directory" and enabling "Move data to a new location".
Now go to the folder you selected and you can delete everything inside the Modified folder. It only contains your patched APKs and some metadata.