UPDATE: After revisiting this, I seem to have misunderstood and misrepresented the particular feature that rolled out earlier this year. Most notably, the new startTrigger block still does not allow you to test URL parameters. It does, however, allow you to set and test headers, a JSON payload, and path parameters.
pathParams- When you create a webhook alias for your workflow such as/orders/{id}/status, users can trigger your workflow viahttps://{domain}/url/orders/{id}/statuswhereidis a dynamic string. You can then access the dynamic path parameters viastartTrigger.pathParams
You can likely refactor your workflow to use path parameters instead of URL parameters, but I'll go back to the team and request that we offer a clear solution for testing the latter as well!
You beat me to it, @khill-fbmc! We rolled this out with the release of version 3.193.0 - there's a quick blurb about the feature here. Definitely let us know if you run into any issues!