I have a Trello board linked to a channel and some Slack Workflow set up.
One of my Slack Workflow allow for creation of ticket and ask some questions, then triggering a message sent to the channel "/trello add [info from quest form]" however this does not trigger a card to be created.
I've tested it multiple time and I can create the tickets myself, in the same manner, however when the text comes from the Slack Workflow, it does not create anything on my board.