[Feature request] Include ability to add invitees to groups through API

Hi, it would be great to add the ability to add invitees to groups through API. 

Unfortunately, it appears it is only possible when the user has accepted the invitation.

The invitee ID returned by the POST] /accounts/{accountId}/invitations  is not similar to the user ID format and is not accepted as an addMembers parameter for the PUT /groups/$GroupID method. 

The impossibility to do so was confirmed by Wrike support.
I am adding it here for trackability.