# List a customer group's customers

`GET /api/v1/customer-groups/{customerGroupId}/customers`

The customers in one group, paged. This is where membership lives, and the group resource deliberately carries no members array: a group with 50,000 buyers would otherwise serialise 50,000 ids into one row of a list response, on a resource whose page cap says nothing about how many people it names. THE OTHER HALF OF THE B2B SYNC PATH is GET /price-lists/{priceListId}/customer- groups. Together they are price list to groups to customers, which is how a wholesale integration learns which buyers get which negotiated prices. Neither leg is useful without the other. THE ROWS ARE THE SAME CUSTOMER RESOURCE /customers serves, with the same fields and the same nullability. One customer has one shape whichever route found them, so a client can hand a row here to the same parser it uses there. CURSOR ONLY, no offset and no total. A merchant tagging customers inserts rows into this membership continuously, and an offset walk drops or repeats one on every page turn; here a dropped row is a buyer who silently stops receiving wholesale prices. AN EMPTY GROUP IS A 200 WITH AN EMPTY PAGE. A group id that does not exist, or belongs to another store, is a 404. The two are distinguished deliberately: a 200 for a mistyped id would record "this tier has no buyers" and apply retail prices to everyone in it. MEMBERSHIP IS READ-ONLY HERE. Nothing on this API adds or removes a member, for the reason the group family publishes no writes at all: a group's price-list targeting rows cascade with it, and a price list left untargeted applies to EVERY customer.

## Path parameters

- `customerGroupId` (string, required)

## Query parameters

- `limit` (integer) — Rows per page. Out of range is a 400 rather than a silent clamp, so a client asking for more than 100 learns it did not get it.
- `after` (string) — The next_cursor from the previous page. Opaque: decode nothing from it and construct nothing by hand, since its encoding is not part of this contract. Omit it to read the first page.

## Responses

- `200` — Success
- `400` — The request was refused before any state changed. `code` is one of:

`invalid_body`, a write body this route will not take. `reason` partitions it
and `field` names the key when one key is at fault.
`invalid_query`, a query parameter, including limit and after.
`invalid_text`, a NUL byte or bytes that are not valid UTF-8 anywhere in the
path, the query or the body. Strip control characters before sending.
`idempotency_key_required`, a write sent without the Idempotency-Key header.
`invalid_request`, an Idempotency-Key longer than 255 bytes.

Routes add their own codes for rules only they know. Switch with a default arm.
- `401` — No credential, or one this API does not accept. `code` is always
`unauthorized`.

THE BODY IS DELIBERATELY UNINFORMATIVE. An expired key, a revoked key, a
publishable key, a key belonging to another merchant and a key that never
existed are all refused with the same bytes, so this response cannot be used to
probe which keys exist. Check the key's state in the dashboard rather than
inferring it here.

Send the key as `Authorization: Bearer <key>` or as `X-API-Key: <key>`. It is
never accepted in a query string.
- `403` — The key lacks the read_customers scope. `code` is `insufficient_scope` and the message names the scope to ask the merchant for.
- `404` — The resource this url addresses does not exist, or never did on this store.

`resource` names the kind of thing that was missing and is the half to branch
on: the code is `not_found` on newer routes and a per-entity spelling on
routes that shipped before that rule, and the two mean the same thing.

A 404 is ALWAYS about the url. An id inside the request body that resolves to
nothing is 422 `unprocessable_reference` instead, so the two cases stay
distinguishable. An id that belongs to a different merchant reads exactly like
one that never existed.
- `429` — Too many requests. `code` is `rate_limited`.

Two limits apply independently: one on the credential and the route family,
one on the client address. The headers describe whichever has less left, so
honouring Retry-After always clears the window that bound.
- `default` — Any status this operation does not list, in the same envelope.

A 5xx means the request may or may not have applied. Retry it with the SAME
Idempotency-Key: that is the only way to find out without risking a duplicate,
and it is what the key is for.

A few 4xx conditions arrive here rather than as a listed status because they
depend on the merchant's plan or on a module being wired: 402 when a quota or a
plan limit is reached, and 503 when a capability the route needs is not
configured on this deployment. Both carry a `code` naming which.

## Example

```bash
curl --request GET \
  --url 'https://api.mercemur.com/api/v1/customer-groups/{customerGroupId}/customers' \
  --header 'Authorization: Bearer <token>'
```