Free and PRO use same code which is common. Only extra feature added on top of free plugin in PRO version.
As multiple recipient is a PRO feature, that part is different in PRO version.
“tokenInput not a function” can be return if tokenInput is not loaded. tokenInput is loaded in footer of the theme. If your theme having issue for footer inclusion that may break it.

Let me know if it works with no other plugin activated and default theme. Then activate your theme and plugins one by one and test.
Let me know if you find any conflict.