Microsoft login: Curl, Postman, and Dotnet work but Node (axios) request returns 404 - node.js

Question

I'm trying to access a graph api (specifically bookings) that only allows the Delegated (work or school account) permission. We need to be able to allow anonymous users to schedule bookings, so we created a fake microsoft user for our server to interact with their api.
I'm able to successfully authorize my user with Postman, Curl, and Dotnet, but I can't get Axios to work for the life of me, even after generating the code from Postman itself. I'm using the same exact URL in each method.
Note: my environment variables don't have typos and I'm running the code in Azure Functions. I know this is a hacky solution, but it seems to be the only way to do it using Microsoft Bookings.
Here's my code:
let data = new FormData();
data.append('grant_type', 'password');
data.append('username', process.env.MICROSOFT_USERNAME);
data.append('password', process.env.MICROSOFT_PASSWORD);
data.append('client_id', process.env.MICROSOFT_CLIENT_ID);
data.append('client_secret', process.env.MICROSOFT_CLIENT_SECRET);
data.append('resource', 'https://graph.microsoft.com/');
data.append('scope', 'https://graph.microsoft.com/.default');
const config = {
method: 'post',
url: `https://login.microsoftonline.com/${process.env.MICROSOFT_TENANT}/oauth2/token`,
headers:
data.getHeaders(),
data: data
};
axios(config).then(resp => {
console.log(resp);
}).catch(e => {
console.log(e);
});