Hello all,
If you are attempting to import your complete FitBit data into Garmin Connect, I have written a program to assist with that. It will convert the entire FitBit history in JSON format to the CSV format that Garmin Connect Web requires. Here is the program, enjoy:
https://www.reddit.com/r/Garmin/comments/12c6b3l/importing_historical_fitbit_data_into_garmin/