At the time of purchase of your BodyTrace scales, you will need to indicate that you will be using FitnessSyncer and they can configure the integration with FitnessSyncer.
Once that is configured, you will need to add a Body Composition Source for each of your scales. In the Identifier field, please enter the serial number of your scale and on the next weighing, we should receive the data shortly thereafter.
We get immediately notified whenever you weigh yourself within their system, and thus, the sync button usually does not find anything.
No, BdoyTrace is currently only available for future weight synchronizations.