getting { code: 120121, message: 'Invalid Custom field index provided.' } while creating contact in zoho inventory

getting { code: 120121, message: 'Invalid Custom field index provided.' } while creating contact in zoho inventory

{
contact_name: String(mobileNumber),
custom_fields: [
{
value: "",
index: 1,
},
{
value: "",
index: 2,
},
{
value: "",
index: 3,
},
],
}
This is my custom_fields 
Please can anyone tell why I am getting this error.

Hoping for fast reply, thanks in advance.