Hi @saint 

1. Refer KB: KB0831254 Mid server running but displaying the error "MID Server not operational (status: Down), po... 

Resolution

This is due to the fact that the source MID Server user credentials copied into the target instance might not match those used by the existing set of MID Servers used by the target. You can view the related documentation below:
https://docs.servicenow.com/csh?topicname=mid-post-clone-issue-resolution.html&version=latest

The resolution to this issue would be to perform the below actions:
1) Stop the current MID Server windows service.
2) Go to the MID server /agent/ folder and open the config.xml file with a text editor such as WordPad.
3) Enter the MID user credentials in the mid.instance.username and mid.instance.password parameters.
4) Start the MID Server windows service.

2. Refer KB: KB0786475 MID Servers and Clones 

3. https://www.servicenow.com/community/itom-forum/miduserconnectivity-mid-server-user-issue/m-p/973077...

4. https://www.servicenow.com/community/itom-forum/mid-server-not-operational-status-down-possibly-due-...