Purchases

Supplier-facing documents and employee costs: bills, expenses, hire purchases, and file attachments on those records.

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Relationship diagram

flowchart TB
  Contact[Contact]
  User[User]
  Project[Project]
  Category[Category]
  StockItem[Stock_item]
  Property[Property]
  Bill[Bill]
  BillItem[Bill_item]
  Expense[Expense]
  HirePurchase[Hire_purchase]
  Invoice[Invoice]
  CapitalAsset[Capital_asset]
  Attachment[Attachment]
  Contact -->|contact| Bill
  Bill -.->|project| Project
  Bill -.->|rebill_to_project| Project
  Bill -->|bill_items| BillItem
  BillItem -.->|project| Project
  BillItem -.->|category| Category
  Bill -.->|rebilled_on_invoice_item| Invoice
  Bill -->|hire_purchase| HirePurchase
  HirePurchase -.->|bill| Bill
  HirePurchase -.->|liabilities categories| Category
  User -->|user| Expense
  Expense -->|category| Category
  Expense -.->|project| Project
  Expense -.->|rebill_to_project| Project
  Expense -.->|rebilled_on_invoice| Invoice
  Expense -.->|stock_item| StockItem
  Expense -.->|property| Property
  Expense -.->|capital_asset| CapitalAsset
  Expense -.->|attachment| Attachment
  Bill -.->|attachment via items| Attachment

Hire purchases are created via the Bills API and exposed as a read-only resource linked back to the originating bill.

Resource catalogue

Resource	Official docs	SDK
Bills	Bills	Not yet
Expenses	Expenses	Not yet
Hire purchases	Hire purchases	Not yet
Attachments	Attachments	Not yet

Key URI fields

Bill

Field	Target	Required on create?
contact	Contact	Yes
project	Project	No
rebill_to_project	Project	No (same as project when rebilling)
rebilled_on_invoice_item	Invoice	Read-only when rebilled

Bill items may set project and category.

List filters: ?contact=, ?project=

Expense

Field	Target	Required on create?
user	User	Yes
category	Category	Yes (or Mileage string)
project	Project	No
rebill_to_project	Project	No
rebilled_on_invoice	Invoice	Read-only when rebilled
stock_item	Stock item	Required when category is purchase of stock
property	Property	Landlord companies only
capital_asset	Capital asset	Read-only on capital purchases

List filter: ?project=

Hire purchase

Read-only. Links to the source bill and liability category URIs.

Attachment

Polymorphic: nested on expenses, bank transaction explanations, and other resources. Fetched by ID via GET /attachments/:id. Access level matches the parent resource.

Cross-cluster links

To cluster	Relationship
Sales	rebilled_on_invoice / rebilled_on_invoice_item when costs are passed through to a client invoice
Foundations	contact, user, category
Projects and time	Optional project for rebilling
Assets and journals	capital_asset on capital purchases
Banking	Bill payment explanations use paid_bill

SDK sequencing note

Bills require Contacts. Expenses require Users and Categories. Rebilling fields matter only after Invoices exist.