Uploading a PBIX file using the import API

Hello,

I am stuck trying to programmatically upload a .pbix file using the import API, making use of the request-promise library which is imported as "rp" here.

I am currently trying the following, which results in HTTP error 400:

let url = 'https://api.powerbi.com/v1.0/myorg/groups/' + groupId + '/imports';
let options = {
	method: 'POST',
	headers: {
		'Content-Type': 'multipart/form-data',
		'authorization': 'Bearer ' + accessToken
	},
	body: fs.createReadStream(__dirname + '/Report.pbix'),
	url: 'https://api.powerbi.com/v1.0/myorg/groups/' + groupId + '/imports'
};

rp(options)
	.then(function (body) {
	console.log('success! ', body);
})
	.catch(function (err) {
	console.log('error', err);
});

I also haven't had any success uploading the file using postman, where I have tried it with and without having set Content-Type. 

What could I be doing wrong?