> ## Documentation Index
> Fetch the complete documentation index at: https://developer.chatsyncs.com/llms.txt
> Use this file to discover all available pages before exploring further.
# Subscriber Assign Custom Fields
> Set one or more custom field values on a subscriber via the ChatSyncs API, using a JSON object of field name/value pairs. Use when a developer asks how to sync CRM data into a subscriber's custom fields.
Sets custom field values on a subscriber. See
[Subscriber Manager's Custom Fields](https://help.chatsyncs.com/docs/custom-fields-labels-lists#custom-fields) for what
a custom field is and the available types (Text, Number, Date, Email, Phone).
## The `custom_fields` JSON format
`custom_fields` is a single JSON object — each **key** is an existing custom field's name, and
each **value** is what you want to set it to, matching that field's type:
```json theme={null}
{
"city": "Bangalore",
"plan_type": "Premium",
"age": 28,
"date_of_birth": "1998-05-20",
"email": "rahul@example.com",
"phone": "919999999999"
}
```
| Field type | Example key | Example value |
| - | - | - |
| Text | `"city"` | `"Bangalore"` |
| Number | `"age"` | `28` (no quotes) |
| Date | `"date_of_birth"` | `"1998-05-20"` (as text, `YYYY-MM-DD`) |
| Email | `"email"` | `"rahul@example.com"` |
| Phone | `"phone"` | `"919999999999"` (as text, digits only) |
Use the names from [Custom Fields List](/developer-api/subscriber/list-custom-fields), or create one first in
**Subscriber Manager → Manage → Manage Custom Fields**. You only need to include the fields you're updating — any field
you leave out is unaffected (verified).
**The API doesn't check what you send.** A field name that doesn't exist is still accepted and stored on the contact
as if it were one, so a typo silently creates a stray value. Types aren't enforced either: an `Email` or `Phone` field
accepts any text. An empty string `""` clears a field. Only invalid JSON is rejected, with
`Invalid JSON:Syntax error`.
## OpenAPI
````yaml POST /whatsapp/subscriber/chat/assign-custom-fields
openapi: 3.1.0
info:
title: ChatSyncs Developer API
version: 1.0.0
description: >-
REST API for sending WhatsApp messages and managing subscribers through
ChatSyncs.
**Authentication.** Send your key as the `apiToken` parameter, or as
`Authorization: Bearer ` — both work on every endpoint **except Custom
Fields List**, which only accepts the `apiToken` parameter (a Bearer header
alone is answered with *The api token field is required.*). A wrong key
returns HTTP 401 `{"status":"0","message":"Unauthenticated."}`; no key at
all redirects to the login page.
**Methods.** Every endpoint accepts both GET and POST with the same
parameters, except Upload Media, which is POST-only. Use POST for anything
that changes data.
**Errors.** Failures usually come back as HTTP 200 with `"status":"0"` and
the reason in `message`, so always check `status`. `status` is the string
`"1"` or `"0"` on most endpoints and a boolean on a few.
**Lists.** Endpoints that return rows put them in `message` as a list; there
is no `data` field (Custom Fields List is the exception and uses `data`).
servers:
- url: https://platform.chatsyncs.com/api/v1
security: []
paths:
/whatsapp/subscriber/chat/assign-custom-fields:
post:
tags:
- Subscriber API
summary: Assign Custom Fields
description: >-
`custom_fields` is a JSON **object**. Each call changes only the fields
you name; the rest are kept (verified). The API does not check that a
field exists, nor its type: an unknown name is stored on the contact as
if it were one, and `Email` or `Phone` fields accept any text. An empty
string clears a field. Use Custom Fields List for the real names.
operationId: assignCustomFields
requestBody:
required: true
content:
application/x-www-form-urlencoded:
schema:
type: object
properties:
apiToken:
type: string
description: >-
Your ChatSyncs API key (not a WhatsApp/Meta access token).
[Where to find
it](/developer-api/finding-ids#api-token-apitoken).
example: API-KEY
phone_number_id:
type: string
description: >-
The WhatsApp account's phone number ID. [Where to find
it](/developer-api/finding-ids#phone-number-id-phone_number_id).
example: PHONE-NUMBER-ID
phone_number:
type: string
description: >-
The subscriber's phone number, with country code, digits
only.
example: PHONE-NUMBER
custom_fields:
type: string
description: A JSON object of custom field names and values.
example: '{"custom_field_name1":"value1"}'
required:
- apiToken
- phone_number_id
- phone_number
- custom_fields
responses:
'200':
description: >-
Standard ChatSyncs response. `status` is `"1"` on success and `"0"`
on failure.
content:
application/json:
schema:
type: object
properties:
status:
type: string
description: '`"1"` = success, `"0"` = failure.'
message:
type: string
description: Human-readable result message.
examples:
success:
summary: Success
value:
status: '1'
message: Subscriber changes have been saved successfully.
error:
summary: A required field is missing
value:
status: '0'
message: >-
The phone number id field is required., The phone number
field is required., The custom fields field is required.
badJson:
summary: custom_fields is not valid JSON
value:
status: '0'
message: Invalid JSON:Syntax error
'401':
description: >-
`apiToken` is wrong. (With no token at all the API redirects to the
login page with HTTP 302 instead of returning JSON.)
content:
application/json:
schema:
type: object
properties:
status:
type: string
message:
type: string
examples:
unauthenticated:
summary: Wrong apiToken
value:
status: '0'
message: Unauthenticated.
````
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