curl --request POST \
  --url https://sandbox.api.fin.com/v1/customers/individual/attach \
  --header 'Authorization: Bearer <token>' \
  --header 'Content-Type: application/json' \
  --data '
{
  "customer_id": "55bd6b4e-c20a-4cc8-9535-91d5557a67d9",
  "proof_of_identity": {
    "type": "PASSPORT",
    "number": "A12345678",
    "country": "USA",
    "issue_date": "2020-01-15",
    "expiry_date": "2030-01-15",
    "files": [
      {
        "uri": "/AbAcQ4hn_0652746727637.pdf",
        "side": "FRONT"
      }
    ]
  },
  "proof_of_address": {
    "type": "UTILITY_BILL",
    "country": "USA",
    "files": [
      {
        "uri": "/AbAcQ4hn_0652746727638.pdf"
      }
    ]
  },
  "tos_policies_value": "e9414388-fbdf-4407-b5c2-bc39eae3645b"
}
'

const url = 'https://sandbox.api.fin.com/v1/customers/individual/attach';
const options = {
  method: 'POST',
  headers: {Authorization: 'Bearer <token>', 'Content-Type': 'application/json'},
  body: JSON.stringify({
    customer_id: '55bd6b4e-c20a-4cc8-9535-91d5557a67d9',
    proof_of_identity: {
      type: 'PASSPORT',
      number: 'A12345678',
      country: 'USA',
      issue_date: '2020-01-15',
      expiry_date: '2030-01-15',
      files: [{uri: '/AbAcQ4hn_0652746727637.pdf', side: 'FRONT'}]
    },
    proof_of_address: {
      type: 'UTILITY_BILL',
      country: 'USA',
      files: [{uri: '/AbAcQ4hn_0652746727638.pdf'}]
    },
    tos_policies_value: 'e9414388-fbdf-4407-b5c2-bc39eae3645b'
  })
};

fetch(url, options)
  .then(res => res.json())
  .then(json => console.log(json))
  .catch(err => console.error(err));

HttpResponse<String> response = Unirest.post("https://sandbox.api.fin.com/v1/customers/individual/attach")
  .header("Authorization", "Bearer <token>")
  .header("Content-Type", "application/json")
  .body("{\n  \"customer_id\": \"55bd6b4e-c20a-4cc8-9535-91d5557a67d9\",\n  \"proof_of_identity\": {\n    \"type\": \"PASSPORT\",\n    \"number\": \"A12345678\",\n    \"country\": \"USA\",\n    \"issue_date\": \"2020-01-15\",\n    \"expiry_date\": \"2030-01-15\",\n    \"files\": [\n      {\n        \"uri\": \"/AbAcQ4hn_0652746727637.pdf\",\n        \"side\": \"FRONT\"\n      }\n    ]\n  },\n  \"proof_of_address\": {\n    \"type\": \"UTILITY_BILL\",\n    \"country\": \"USA\",\n    \"files\": [\n      {\n        \"uri\": \"/AbAcQ4hn_0652746727638.pdf\"\n      }\n    ]\n  },\n  \"tos_policies_value\": \"e9414388-fbdf-4407-b5c2-bc39eae3645b\"\n}")
  .asString();

import requests

url = "https://sandbox.api.fin.com/v1/customers/individual/attach"

payload = {
    "customer_id": "55bd6b4e-c20a-4cc8-9535-91d5557a67d9",
    "proof_of_identity": {
        "type": "PASSPORT",
        "number": "A12345678",
        "country": "USA",
        "issue_date": "2020-01-15",
        "expiry_date": "2030-01-15",
        "files": [
            {
                "uri": "/AbAcQ4hn_0652746727637.pdf",
                "side": "FRONT"
            }
        ]
    },
    "proof_of_address": {
        "type": "UTILITY_BILL",
        "country": "USA",
        "files": [{ "uri": "/AbAcQ4hn_0652746727638.pdf" }]
    },
    "tos_policies_value": "e9414388-fbdf-4407-b5c2-bc39eae3645b"
}
headers = {
    "Authorization": "Bearer <token>",
    "Content-Type": "application/json"
}

response = requests.post(url, json=payload, headers=headers)

print(response.text)

package main

import (
	"fmt"
	"strings"
	"net/http"
	"io"
)

func main() {

	url := "https://sandbox.api.fin.com/v1/customers/individual/attach"

	payload := strings.NewReader("{\n  \"customer_id\": \"55bd6b4e-c20a-4cc8-9535-91d5557a67d9\",\n  \"proof_of_identity\": {\n    \"type\": \"PASSPORT\",\n    \"number\": \"A12345678\",\n    \"country\": \"USA\",\n    \"issue_date\": \"2020-01-15\",\n    \"expiry_date\": \"2030-01-15\",\n    \"files\": [\n      {\n        \"uri\": \"/AbAcQ4hn_0652746727637.pdf\",\n        \"side\": \"FRONT\"\n      }\n    ]\n  },\n  \"proof_of_address\": {\n    \"type\": \"UTILITY_BILL\",\n    \"country\": \"USA\",\n    \"files\": [\n      {\n        \"uri\": \"/AbAcQ4hn_0652746727638.pdf\"\n      }\n    ]\n  },\n  \"tos_policies_value\": \"e9414388-fbdf-4407-b5c2-bc39eae3645b\"\n}")

	req, _ := http.NewRequest("POST", url, payload)

	req.Header.Add("Authorization", "Bearer <token>")
	req.Header.Add("Content-Type", "application/json")

	res, _ := http.DefaultClient.Do(req)

	defer res.Body.Close()
	body, _ := io.ReadAll(res.Body)

	fmt.Println(string(body))

}

{
  "data": {
    "customer_id": "55bd6b4e-c20a-4cc8-9535-91d5557a67d9"
  }
}

{
  "message": "Authentication failed"
}

{
  "message": "<string>",
  "errors": [
    {}
  ]
}