Problem
You are running mars on the ECMWF cloud, and your request is stuck, an the last message is similar to:
mars - INFO - 20230627.103107 - Calling mars on 'mars.ecmwf.int', local port is 50801 mars - INFO - 20230627.103107 - Callback at address 192.168.1.X, port 50801
Solution
MARS client does not know your external IP address, so it only listens for the server to contact on a private (192.168.1.X) IP address which MARS servers cannot reach. This may be the case if your VM is set up attached only to the private network, with or without Floating IP.
If your VM does not have an external IP, you will have to provision a new one. Follow the steps in Provision a new instance - web to provision a new Virtual Machine, making sure that the VM will be reachable on a public IP, either by attaching it to the external-internet public network, or giving it a floating ip if only attached to the private one.
If your VM its setup attached to the external-internet public network, then everything should work from now
Additional steps for VMs with Floating IPs
If your VM is setup with a private network and external Floating IP, then you will need to tell the mars client what your IP address is via the following environment variable:
export MARS_DHS_LOCALHOST=<your_public_ip>
You will need to have that variable defined on every session that you need to run MARS from. You may add that definition into your .bashrc or .profile scripts.