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Operation Monitor app is getting failed due to below reason:
If the connection is available in the QMC, you shall then be able to use it.
Only thing I see now out the configuration of the connection (still looking for localhost) is that maybe a security rules is blocking you.
Have you created any specific security rules on your platform ?
What is your role on the QMC ?
Let's then perform a check.
In the hub, open an app, go to the script editor and on the right hand side, check if the data connection is available in the data connection list. (if you are confortable with auditing in the QMC, you shall also be able to do the same check with QMC audit functions)
If not, you have a right issue else, it can be an issue on your installation, connector configuration...
do you have connection rights?
in the script do you have the connection?
when you go to the QMC, in Data connection, see the security rules.
The connection in the beginning is assigned to the account that executes Qlik services
if you don't have the rights, create security rules.
+1 according to previous test, you have two options
Create or update security to allow your user or if you're making simple tests just allocate the data connection to you (ownership change)