Related Action passing 1 parameter instead of 2

I'm getting the following error message on a related action to a record I created:

An Error Has Occurred An error occurred while applying the context for the CTM External User List related action [identifier=67]. Details: Expression evaluation error at function rule!CTM_AddUpdateExternalUsers: Rule 'ctm_addupdateexternalusers' has 2 parameters, but instead passed 1 parameters.

The process model only has 1 parameter, so I'm not sure where it's referring to having 2 parameters? 

Thanks for suggestions on where to solve this issue.

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