Hi @23drive, welcome to the Mattermost forums and sorry for the late reply!
Glad to hear you found the error, just FTR: a 404 generated by the API almost always means, that there’s a typo in the URL, so this should be the first check then.
I cannot tell if this was always the name of this API endpoint, but according to the documentation, there does not seem to be a recent change:
https://api.mattermost.com/#tag/integration_actions/operation/OpenInteractiveDialog
Did you find the wrong endpoint in some documentation that should be fixed?