> ## Documentation Index
> Fetch the complete documentation index at: https://docs.syntage.com/llms.txt
> Use this file to discover all available pages before exploring further.

# Customers and suppliers

> Identify an entity's counterparties from invoices and measure how its sales or purchases are distributed among them.

Syntage identifies an entity's customers and suppliers from its [SAT invoices](/resources/datasources/sat/invoices). These counterparties are not standalone resources: each one is the issuer or receiver of an invoice associated with the entity.

## How counterparties are identified

| Relationship | Invoice direction      | Counterparty |
| ------------ | ---------------------- | ------------ |
| Customer     | Issued by the entity   | Receiver     |
| Supplier     | Received by the entity | Issuer       |

Issued invoices show who buys from the entity. Received invoices show who sells to the entity. Use the individual invoices when you need transaction details, or a concentration view when you need totals and relative share by counterparty.

## Using the dashboard

1. Open [All Entities](https://app.syntage.com/entities) and select the entity.
2. To review individual transactions, open **Data > Invoices**. For an issued invoice, the receiver is the customer; for a received invoice, the issuer is the supplier. Use **Filters** to narrow the table by issuer or receiver name or RFC.
3. To compare totals and share by counterparty, open **Reports** and view the **Customer Concentration** or **Vendor Concentration** insight in a report.

Customer and supplier concentration insights aggregate invoice totals by counterparty. Each result includes the counterparty's RFC and name, total invoiced amount, share of the entity's sales or purchases for the selected period, and a transaction series over time.

Use these insights when you need to identify dependency on a small number of customers or suppliers.

## Using the API

List invoices with `isIssuer=true` to find customers and `isReceiver=true` to find suppliers. To find transactions with one counterparty, filter by `issuer.rfc`, `issuer.name`, `receiver.rfc`, or `receiver.name`.

| Task                            | Endpoint                                                                                                                                       |
| ------------------------------- | ---------------------------------------------------------------------------------------------------------------------------------------------- |
| List and filter invoice records | [`GET /entities/{entityId}/invoices`](/api-reference/ds-mx-sat-invoices/list-all-entities-invoices)                                            |
| Measure customer concentration  | [`GET /entities/{entityId}/insights/customer-concentration`](/api-reference/customer-concentration-insight/get-customer-invoice-concentration) |
| Measure supplier concentration  | [`GET /entities/{entityId}/insights/supplier-concentration`](/api-reference/vendor-concentration-insight/get-vendor-invoice-concentration)     |