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POST
Assign Custom Fields
Sets custom field values on a subscriber. See Subscriber Manager’s 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:
The field must already exist — check Custom Fields List for valid names, 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.

Body

application/x-www-form-urlencoded
apiToken
string
required

Your ChatSyncs API key (not a WhatsApp/Meta access token). Where to find it.

Example:

"API-KEY"

phone_number_id
string
required

The WhatsApp account's phone number ID. Where to find it.

Example:

"PHONE-NUMBER-ID"

phone_number
string
required

The subscriber's phone number, with country code, digits only.

Example:

"PHONE-NUMBER"

custom_fields
string
required

A JSON object of custom field names and values.

Example:

"{\"custom_field_name1\":\"value1\"}"

Response

200 - application/json

Standard ChatSyncs response. status is "1" on success and "0" on failure.

status
string

"1" = success, "0" = failure.

message
string

Human-readable result message.