I encountered this when trying to build my react native app on windows, also on my Mac and the solution(Mac) is.. open your command prompt and type
then add the following in the file and save
export ANDROID_HOME=$HOME/Library/Android/sdk export PATH=$PATH:$ANDROID_HOME/emulator export PATH=$PATH:$ANDROID_HOME/tools export PATH=$PATH:$ANDROID_HOME/tools/bin export PATH=$PATH:$ANDROID_HOME/platform-tools
then still in the command prompt type
there you go.