I believe that in order for the script to post output you need to use | Table, or the request format is not valid. There was a great blog post on it by Lisa Rushworth here https://www.rushworth.us/lisa/?tag=splunk
I have taken some of her suggestions, added in proxy support and compiled it in another version of this app that works for all outputs here: https://github.com/cottinghamd/Splunk-Microsoft-Teams-Webhook-Connector
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