As pointed out by Thiago Luiz Domacoski , to publish a new APK on Google Play, the value of the versionCode in your gradient, must be greater than the value of the last APK that is published.
defaultConfig {
/* ... */
versionCode 2 // <---- Número da versão do app
versionName "nome da versao"
/* ... */
}
To know the versionCode value of the latest published version of an app:
Open the Google Play Developer Console
Select an app
Select Version Management from the side menu
Click Apps Versions on the submenu
In the information that appears, look for APK version code . This is your last versionCode used, so the next version you publish for this app should have a number larger than that.