Zoho inventory returning "Internal Server Error"

I am trying to push existing data to Zoho via API calls and that is not working.

https://inventory.zoho.com/api/v1/items?authtoken=*****&organization_id=***** returns

{"code":6,"message":"Internal Error"}

To insert, I am doing the following

const params = {
authtoken: '******',
organization_id: *****,
JSONString: JSON.stringify({ contact_name: 'Bowman and Co' }),
};

HTTP.post('https://inventory.zoho.com/api/v1/contacts',
{
params,
},
(err, response) => {
if (err) {
return console.error('upload failed:', err);
}
console.log('Upload successful!  Server responded with:', response);
return response;
})

response: { statusCode: 400,content: '{"code":2,"message":"The request passed is not valid."}',