Sync endpoint to create, update, and archive connection sources.
Connection sources organize transactions (for example, by bank account; or to separate bills and invoices)
Labels allow seamless reference to the chart of accounts within the Ledger.

Each request must include the complete set of sources for this connection.
When omitted from a subsequent sync, existing sources become archived and their data remains in the ledger.
Archived sources are excluded from List Sources. Syncing the same external_id again reactivates the source.

Requires scope: source:sync.