ERR_TUNNEL_CONNECTION_FAILED on localhost testing

I have an Angular project running with the command ng serve --configuration lambdatest --host 0.0.0.0 --disable-host-check. I’ve configured an underpass tunnel and proxy. The proxy appears to be working because I can see that Lambdatest has downloaded the default config file.

I have a localhost page at https://localhost:4200. When I try to run a ‘Real Time’ test on this page using https://localhost.lambdatest.com:4200, I encounter the following error:

This site can’t be reached The webpage at https://localhost.lambdatest.com:4200/ might be temporarily down or it may have moved permanently to a new web address. ERR_TUNNEL_CONNECTION_FAILED

Neither https://localhost:4200 nor 10.0.0.5:4200 seem to be working.