post
https://{youraccountname}.api-us1.com/api/3/accountCustomFieldData
Give one company account its first value in an account custom field. To change a value the account already holds, update that value by its id with PUT /accountCustomFieldData/{id}.
{
"accountCustomFieldDatum": {
"accountId": "2",
"customFieldId": "1",
"fieldValue": "test title"
}
}{
"accountCustomFieldDatum": {
"id": "5",
"accountCustomFieldMetumId": 1,
"accountId": 2,
"customFieldId": 1,
"createdTimestamp": "2018-11-06 02:27:05",
"updatedTimestamp": "2018-11-06 02:27:05",
"fieldValue": "test title",
"links": {
"account": "https://:account.api-us1.com/api/:version/accountCustomFieldData/5/account",
"accountCustomFieldMetum": "https://:account.api-us1.com/api/:version/accountCustomFieldData/5/accountCustomFieldMetum"
}
}
}