The following article explains in detail how to verify if there is connectivity between the Docker container in which BlazeMeter's on premise agent is installed to BlazeMeter's API endpoint.
To check for connectivity to the BlazeMeter API servers from inside a container use the following command:
$ sudo docker run -it blazemeter:latest curl https://a.blazemeter.com/api/v4/tests
It should result in a JSON output:
Once you have verified the above use the following commands to remove the container that is created by the above command:
$ sudo docker ps -a (Get the container ID for the blazemeter:latest container)
$ sudo docker rm <Container ID> (Removes the container)