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Regarding this post, I can try and assist! To start, which SolarWinds product(s) are using?
I am having the same issue. We are using Solarwinds NPM, SAM and NCM
Are you trying the simulate action or are you forcing the the status of the object being monitored to the state that would trigger the alert?
I don't think simulate can be used to trigger a POST action.
What I do is add a node that I can manipulate, then make a change that can force the trigger. You can either make a copy of the alert you wan to test and or scope the alert to only be the object you want to test.
To test the alert firing and performing a POST action. I edit the alert and go to the summary page, if you trigger condition exists it should say "This Alert will immediately trigger....."
If that's working as you want, click submit and you should be able to force a POST for your integration.