Its a hassle to manually sign your APK's after you build them, you should definately automate this.
Its so simple, heres how:
Firstly create a keystore file if you haven't already:
# platforms/android/release-signing.properties
storeFile=/path/to/yourName.keystore
keyAlias=your_alias_name
# add these too if you dont want to manually enter your keystore and key password every time
storePassword=your_keystore_password
keyPassword=your_key_password
Now they will be signed during the build process with ionic build --release android
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