In order to sync account properties you must first have users synced into your Heap workspace.
The reason for this is that in order to sync account properties you must first configure Account IDs.
This may be done by navigating to Account > Manage > Features and reading the following:
"To analyze accounts in Heap, you need to specify a user property that can be used to group users into accounts (e.g. Account ID)."
You may also specify the timestamp of the event in your source. However, be aware that this value
may be overridden by its respective mapping and is completely optional. If you choose not to explicitly specify
a timestamp then Heap will use the time the event arrives to the server.