Filtering on xAPI statements using agent attribute

I am trying to filter on a GET xAPI statment using few attributes. I was successful using verb, since, upto parameters, but I am failing to properly use agent param.

I understand that agent param should be a json object, but Docebo’s xAPI always gives me empty response when I tried adding this param.

 Attaching few screenshots of success and failures.

success :https://{{domain.name}}.docebosaas.com/tcapi/statements?since=2022-06-01&until=2022-06-07T17:07:56.780Z

with agent param

https://{{domain.name}}.docebosaas.com/tcapi/statements?since=2022-06-01&until=2022-06-07T17:07:56.780Z&agent='{"mbox":"mailto:sxxxxxxxxi@xyz"}'

I tried multiple variations - adding a url encoded string, adding object type etc.. Nothing worked.

If any one was successful in using an agent filter, do let me know