Please make sure that you have neccessary tools installed for android such as
SDK and build tools with 27
i.e mentioned in build.gradle
buildToolsVersion = "27.0.3"
minSdkVersion = 19
compileSdkVersion = 27
targetSdkVersion = 27
supportLibVersion = "27.1.1"
Also note that i am using react-native 0.56.0 that is latest for now, with upgraded gradle 3+ with 4.4 distributions distributionUrl=https\://services.gradle.org/distributions/gradle-4.4-all.zip