Zoho Projects API Timesheet - General Error 6500 - Adding time entry - php

Question

Integration: Active Collab - Zoho Projects
I'm trying to create a new Time entry under a task in Zoho Projects, using the API.
I've already synced up tasks and projects. But I'm having a hard time creating a time entry.
I've tried with php and with postman. On both ends I get the same error:
Response HTTP Status Code : 400
{"error":{"code":6500,"message":"General Error"}}
Here's my request:
$request_parameters = array(
'authtoken' => 'APITOKEN',
'date' => '02-20-2018',
'bill_status' => 'Billable',
'hours' => '02:22'
);
These are being passed as URL parameters.
If I change any of the parameters the error code changes.
I'm using the example provided in the Zoho Project documentation page:
Not sure what's up.
Here's the request URL:
https://projectsapi.zoho.com/restapi/portal/hidden_portal_id/projects/1167980000000355033/tasks/1167980000000355033/logs/?authtoken=hidden_api_token&date=02-20-2018&bill_status=Billable&hours=02%3A22
I've found a similar thread but could not figure it out based on that
Thanks.
Here's the full code:
/* Set the Request Url (without Parameters) here */
$request_url = 'https://projectsapi.zoho.com/restapi/portal/hidden_portal_id/projects/'.$endpoint;
$ch = curl_init();
curl_setopt($ch, CURLOPT_RETURNTRANSFER, TRUE);
$request_parameters = array(
'authtoken' => 'hidden_api_key',
'date' => '02-20-2018',
'bill_status' => 'Billable',
'hours' => '02:22'
);
curl_setopt($ch, CURLOPT_POST, TRUE);
curl_setopt($ch, CURLOPT_POSTFIELDS, http_build_query($request_parameters));
//I've added this line because I've found a similar error 6500 thread see the link above
$request_url .= '?'. http_build_query($request_parameters);
/* Here you can set the Response Content Type */
curl_setopt($ch, CURLOPT_HTTPHEADER, array('Accept: application/json'));
/* Let's give the Request Url to Curl */
curl_setopt($ch, CURLOPT_URL, $request_url);
/* Allows Curl to connect to an API server through HTTPS */
curl_setopt($ch, CURLOPT_SSL_VERIFYPEER, false);
curl_setopt($ch, CURLOPT_HEADER, TRUE);
d($request_parameters,$request_url);
/* Let's get the Response ! */
$response = curl_exec($ch);
$response_info = curl_getinfo($ch);
/* Don't forget to close Curl */
curl_close($ch);