New Zoho Projects Time entry in API - General Error - 6500

New Zoho Projects Time entry in API - General Error - 6500

Hi there,

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 result:
{"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.
Not sure what's up.

Thanks.