CB Content Bot 3.0.1 in IFrame Wrapper URL

I'm trying to use CB Content to put a secret CB field into a URL of a system IFRAME menu item, like an API Key unique to each user, to link to an external system outside of Joomla.

In the menu item, for the IFrame SRC option, I put in:

src="https://path/to/link?api={cb}[cb_api]{/cb}"

It does not substitute though. Another plug-in I have replaces {niceuserinfo} with the username in the URL. Is this not possible with CB Content Bot, to have it substitute a CB field in a Joomla IFrame Wrapper Menu Item?

I know the CB Content Bot works--I can do this substitution in an article, but not in the IFrame URL...

OH! The other plugin is a System plugin. CB Content Bot is a Content plugin. Is that why it doesn't work? Any ideas?

CB Content Bot is designed to allow substitution support for Joomla content. It's not designed for or tested in any other content prepare scenarios. As far as I'm aware content prepare is never ran on the wrapper menu item url and the one extension you have that does work for it is possibly doing the replacement by other means (acting on routing or menu item triggers). You should be able to just put an iframe in a Joomla article then link to that article though as a workaround.