> ## Documentation Index > Fetch the complete documentation index at: https://docs.upwell.com/llms.txt > Use this file to discover all available pages before exploring further. # Accounts receivable API > The objects you touch to automate receivables — creating customer invoices, delivering them, and applying the payments that come back. **Accounts receivable is money in**: getting your customers paid up, quickly. Upwell's job is to get an accurate invoice out the door and then apply the cash that comes back to the right invoices. The endpoint reference is alphabetical, which is deliberately neutral but doesn't tell you what belongs together. This page does. For the payables side, see [Accounts payable API](/api-reference/ap-overview). ## The lifecycle You create an **invoice** for a customer and link the **shipments** it bills. New invoices start in `CREATED`. **Invoice line items** carry the priced rows — line haul, fuel, accessorials — and sum to the invoice total. Rules and exceptions can hold an invoice back. Once it's clean it's approved for sending — either automatically or through the **invoice approval** queue. Delivery happens by email, customer portal, EDI, or print — or the invoice is rolled into a statement or list bill instead of being sent alone. A **customer payment** records what arrived. Its **line items** say which invoices the money applies to, moving each to `PART_PAID` or `PAID`. ## The objects | Object | What it does | | ------------------------------- | -------------------------------------------------------------------------------------------------------------------- | | **Invoices** | What you bill your customer. An unqualified "invoice" always means this one. | | **Invoice Line Items** | The priced rows. They sum to the invoice total. | | **Invoice Shipments** | Which shipments an invoice bills. Use these endpoints to add or remove one *after* the invoice exists. | | **Invoice Documents** | Supporting paperwork on the invoice. Documents on a linked shipment appear automatically. | | **Invoice Approval** | The queue of invoices waiting for sign-off before delivery. | | **Customer Payments** | An incoming remittance — what arrived, and on which check or ACH. | | **Customer Payment Line Items** | How that money splits across invoices. This is what makes cash application work when one check covers many invoices. | **Invoice vs. carrier invoice** — same word, opposite directions of money. An **invoice** (`inv_`) is you billing your customer. A **carrier invoice** (`cari_`) is a carrier billing you. Throughout these docs an unqualified "invoice" is always the customer one. See [Core concepts](/concepts/data-model). Line-item amounts **need not** sum to the payment total. A remittance can be partially applied and reconciled later, so don't treat a shortfall as an error. ## Before any of this works Receivables reference records that have to exist first: * **Customers** — who you bill. Sync before invoices. Note that deleting a customer also deletes their invoices, so deactivate instead. * **Shipments** — the load being billed. * **Documents** — how supporting paperwork gets attached. * **Rules** — optional, but this is how you hold invoices that shouldn't go out yet. See [Syncing foundation entities](/api-guides/syncing-foundation-entities). ## Guides for this side Create invoices, add line items, attach documents, link shipments. Create a remittance with its line items and reconcile it. The AR dashboard, aging, and collections workflow. How remittance data arrives and gets matched. Automated follow-up on overdue invoices. Let customers pay from the portal.