(Disclaimer: I got the same error in iOS. As it is not clear in which operating system you have the problem, I will put my grain of sand here.)
In my particular case, it was caused because I removed
localhost entry from
Info.plist. This is required for development / troubleshooting.
This is what this section looks like:
NSAppTransportSecurity NSAllowsArbitraryLoads NSExceptionDomains localhost NSExceptionAllowsInsecureHTTPLoads