Unable to fecth files and folders from Team folders

Thank You for your reply: Please see my code and process I followed below:

1. STEP1: First I tried to find the the namespace ID's of the folder I have creared. I got the following output when I executed the API:

https://api.dropboxapi.com/2/team/namespaces/list

[namespaces] => Array
(
[0] => Array
(
[name] => Your team's shared workspace
[namespace_id] => 6131728736
[namespace_type] => Array
(
[.tag] => team_folder
)

)

[1] => Array
(
[name] => Sales
[namespace_id] => 6131729056
[namespace_type] => Array
(
[.tag] => shared_folder
)

)
[2] => Array
(
[name] => Custom_team_folder
[namespace_id] => 6512687312
[namespace_type] => Array
(
[.tag] => shared_folder
)

)

-----------------------------------------------------------------------------------------------

2. STEP2: Then I call this API https://api.dropboxapi.com/2/files/list_folder and passed the Namespace Id "6512687312" into my code, to get the list of files and folder present into the "Custom_team_folder" .
But I got this error:
"Operation completed without any errorsError in call to API function "files/list_folder":
This API function operates on a single Dropbox account, but the OAuth 2 access token you provided is for an entire Dropbox Business team. Since your API app key has team member file access permissions, you can operate on a team member's Dropbox by providing the "Dropbox-API-Select-User" HTTP header or "select_user" URL parameter to specify the exact user."

Could I know How can I solve this error, why I am getting this error

This is My code: I used CURL using PHP:

<?php

$data = array("path"=>'');
$payload = json_encode($data);

$ch = curl_init('https://api.dropboxapi.com/2/files/list_folder');

curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
curl_setopt($ch, CURLINFO_HEADER_OUT, true);
curl_setopt($ch, CURLOPT_POST, true);
curl_setopt($ch, CURLOPT_POSTFIELDS,$payload);

$headers = array(
'Content-type: application/json',
'Dropbox-API-Path-Root: {".tag": "namespace_id", "namespace_id": "6512687312"}',
'Authorization: Bearer <REDACTED>',
);

curl_setopt($ch, CURLOPT_HTTPHEADER, $headers);

if(curl_exec($ch) === false)
{
echo 'Curl error: ' . curl_error($ch);
}
else
{
$result_file_names = curl_exec($ch);
echo 'Operation completed without any errors';
}
print_r($result_file_names);

curl_close($ch);

exit;

?>

Please see the screen shot for more reference:

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I hope I will get the solution now.