Hello @Juan Mesa Sierra Thank you for reaching out to us on Microsoft Q&A platform. Happy to help!
Based on the details provided, I understand that you are trying to set up the Azure migrate discovery appliance but if failed validation. We use remote SSH commands from appliance to run commands. So, first thing, you need to check if you can ssh to the target VM which you wanted to discover from appliance.
Further more, try these two options: you can use option 1 (Sudo account) or option 2 (set cap). Refer to the guidance here - https://video2.skills-academy.com/en-us/azure/migrate/tutorial-discover-physical#prepare-linux-server
Hope this will help resolve the issue. Let us know if you need further assistance!
If the response helped, do "Accept Answer" and up-vote it