The niche are 1-2 people service firms that work with clients on a schedule. So this is more of an infrastructure utility for a specific type of company rather than an entire vertical. For cold calling did you use a firm to do this?
Have you thought about targeting a sub-niche, to try to get some traction, before going broad?
For example, Dentist's offices: if you were to call and visit a few local dentists, see if there are any customizations that would help them specifically (like recurring appointments a year in advance, etc.) and then brainstorm with them to see how they would recommend you advertising to their colleagues.
Once you get some traction in one vertical, you can leverage it to the next one.
Thank you for the links.