Firstly, you must attach the potential candidate to a job before sending him or her an InMail. To make it easy, check the reference of the job in SmartRecruiters to look for the right job to connect the profile with.
For your information, SmartRecruiters will synchronize candidate’s information (email address, phone number, experience, education, InMails exchange, Notes) when the candidate agrees to share it. In return, the new application, reviews and notes will be synchronized back to Linkedin Recruiter.
If you cannot connect profiles to any jobs, please feel free to make a ticket on IT Portal, due to the big number of Linkedin Recruiter seats created, yours may not be activated yet.