Sorry Katya, but did you read the error at all ?
pre Error: '_id' is missing for pointer column 'groupType ( @ 66 : 18 ) - throw e/pre
The error is about the pointer column of the collection groups, and the fact its missing the _id. Using this in the app works perfectly, but for some reason its not working in server code. 'groupType' is sent via the app and sent to the server code service under the name 'groupTypeID'. Which is shown its sending it in console.log, and moved to 'group_type_id'.
I honestly do not understand your post at all, or how it could help fix this error!?!