> ## Documentation Index > Fetch the complete documentation index at: https://docs.gigstack.io/llms.txt > Use this file to discover all available pages before exploring further. # Understand a sale in five minutes > Know which record to create, when money moves, and when a CFDI exists. This guide explains **Mexican CFDI**. For Colombian identification and invoice fields, read [Colombia](/countries/colombia); for common API fields, read [Shared fields](/concepts/shared-fields). You sell one hour of consulting for **MXN 1,000 plus MXN 160 of IVA**. The customer pays **MXN 1,160**. Start with that sale; choose the API operation that matches what has actually happened. | What happened? | What to create | Small example | | - | - | - | | You know who the customer is. | **Client** | Save their contact and fiscal details once. | | You want to review a bill before issuing it. | **Invoice draft** | Save the consulting line and preview its PDF. | | You are ready to issue the fiscal document. | **Income invoice**, CFDI type `I` | Stamp the draft and save the returned UUID. | | The customer already sent the money. | **Registered payment** | Record the MXN 1,160 bank transfer. | | You want the customer to pay through a link. | **Payment request** | Create a checkout link; wait for payment confirmation. | | The customer will provide fiscal details later. | **Receipt** | Give them a self-invoicing link. | | A customer pays an invoice you issued on credit. | **Payment complement**, CFDI type `P` | Link the amount received to the original invoice UUID. | | You need a credit note for a return or discount. | **Egress invoice**, CFDI type `E` | Reference the original invoice. | A registered payment records money already received. An invoice records the fiscal sale. These are separate records; the API can automate the relationship when you explicitly request it. ## Three IDs you will use | Value | What it identifies | Where to get it | | - | - | - | | `client_...` | A saved customer | `data.id` from `POST /clients` | | `inv-draft_...` | A document you can still edit | `data.id` from `POST /invoices/draft` | | A UUID such as `00000000-0000-4000-8000-000000000001` | A stamped CFDI | `data.uuid` from the stamping response | After stamping a draft, use the **returned UUID** to fetch the invoice. Do not assume the old draft ID is the issued invoice's ID. The draft-stamping response can omit `data.id`. ## The fiscal words, translated into decisions * **CFDI**: the Mexican electronic fiscal document. Its XML contains the fiscal data; a PDF is a readable representation. * **Timbrar / stamp**: issue the CFDI through the invoicing provider. A saved draft has not completed this step. * **RFC**: the tax identity of the issuing business or recipient. * **Uso CFDI (`use`)**: the recipient's stated fiscal use of the document. Ask them; a code in an example is not a default for every customer. * **Régimen fiscal (`tax_system`)**: the recipient's registered tax regime. * **Forma de pago (`payment_form`)**: how money was paid, such as `03` for bank transfer. * **Método de pago (`payment_method`)**: whether the invoice is paid in one payment (`PUE`) or deferred / in installments (`PPD`). ## Paid now or paid later? For the simple **already paid in full** example, use `PUE` with the actual payment form. For a sale **unpaid when you issue the invoice**, the ordinary flow is `PPD` with `99` (por definir), followed by a payment complement when payment arrives. Special fiscal cases have additional rules; these recipes cover the ordinary flows. The SAT explains the fields in its [CFDI filling guides](https://www.sat.gob.mx/minisitio/Factura/emite_materialdeayudaparafactura.htm) and [payment-complement guidance](https://wwwmat.sat.gob.mx/cs/Satellite?c=ConsultaInfo\&childpagename=SatTyR%2FConsultaInfo%2FSAT_LandingConsultaInformacion\&cid=1462228892764\&packedargs=d%3DTouch\&pagename=TySWrapper). Follow one consulting sale from customer to CFDI. Record a payment without creating another invoice. This documentation is built and hosted on [Mintlify](https://mintlify.com), a developer documentation platform.