Lists the unsettled open bills a location's POS registers are currently holding in the realtime bill store (saved-but-not-settled restaurant/retail bills). Pass the literal string all as the id for every location. Requires the p/r-bill permission on the location (company-wide for all). Each item carries id, location, register, number, total, raw (the full client bill payload), version, synced_at, created_at and updated_at; the sandbox had no open bills when this example was captured.