This is going to be the case for a number of spells until healbot is fully updated with all of the old spells and spell ids. I will pull the latest version of the code and see what i can do to help out with adding some of them, as i have already begun doing so on my copy and have dispel magic and cure disease working.
Here is a working fix that allows you to enter the ranked spells in the format "Lesser Heal(Rank 1)".
Edit HealBot_Action.lua and replace the function HealBot_Action_GetSpell with the following:
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