I was having this problem with Android Studio when I'm behind a proxy. I was using Crashlytics that tries to upload the mapping file during a build.
I added the missing proxy certificate to the truststore located at /Users/[username]/Documents/Android Studio.app/Contents/jre/jdk/Contents/Home/jre/lib/security/cacerts
with the following command: keytool -import -trustcacerts -keystore cacerts -storepass [password] -noprompt -alias [alias] -file [my_certificate_location]
for example with the default truststore passwordkeytool -import -trustcacerts -keystore cacerts -storepass changeit -noprompt -alias myproxycert -file /Users/myname/Downloads/MyProxy.crt
