The complete set of Sources for this connection. Connections which write data must have at least one source.
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.
A source represents a single account in the source system, such as a bank account or credit card. Each source may have different Labels.
Implementers may treat sources as logical groupings of transactions with similar configurations, such as "Bills" or "Invoices".

Entity to scope the request to. Required for service-account and organization-app tokens.
Sync sources for each entity before other source writes; each entity has its own connection.