I am using flutter and received this error out of nowhere. So, what basically happens is that the lines within your dependencies within android/build.gradle file such as:
classpath 'com.android.tools.build:gradle:4.1.0' classpath "org.jetbrains.kotlin:kotlin-gradle-plugin:$kotlin_version"require certification that the grade file downloads from the internet. But when there is something that's blocking the gradle to download those certificates, this is typically shown.
I tried exporting the certificate and adding it manually but it didn't seem to work for me. What worked for me, after countless head scratches, was disabling the proxies from your network preferences. It was somewhere mentioned that disabling Charles Proxy would fix it but at that moment, I was clueless what Charles was and what proxy was. And in my case, I did not have the Charles proxy thing so I went on with finding the proxies in the network preferences settings in Mac( it could be found somewhere in network settings for Windows). I had Socks enabled within the proxy. I disabled it and then again rebuilt the gradle and TA-DAH!!! It worked butter smooth.
There are a few things to remember. If you build your project right after disabling proxy without closing the network preferences tab, the disable proxies won't work and it will show the same error. Also if you've already built the project and you're running it again after disabling proxies, chances are it's gonna show the same error( could be due to IDE caches). How it worked for me: Restart the Mac, open a few tabs in the browser( for a few network calls), check the network preferences from system preferences>> wifi and disable proxies, close the system preferences app, and build the project.