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

# Get a customer

> Fetch a single customer by externalId (recommended) or LMS id.

Two equivalent forms. **Prefer the externalId form** — it lets you read a
customer by the reference you already store, with no client-side mapping
to a numeric LMS id. See [Addressing a customer](/customers/overview#addressing-a-customer).

## Path parameters

<ParamField path="customer_external_id" type="string" required>
  The customer's partner-supplied externalId (the value you sent on
  create). On the alternative `/v1/customers/{customer_id}` form, this is
  the numeric LMS id instead.
</ParamField>

## Examples

```bash theme={null}
# By externalId (recommended)
curl -sf "$BASE/v1/customers/external/ext-ada-001" \
  -H "Authorization: Bearer $TOKEN"

# Same effect, by LMS id
curl -sf "$BASE/v1/customers/42" \
  -H "Authorization: Bearer $TOKEN"
```

## Response

`200 OK` returns the full [customer object](/customers/overview).

## Errors

| Code               | When                                                                              |
| ------------------ | --------------------------------------------------------------------------------- |
| `not_found`        | No customer exists with that externalId or id                                     |
| `invalid_argument` | `customer_id` is not a valid numeric identifier (only applies to the LMS-id form) |