Keep getting 500 error when trying to create invoice.

Everything was working for a while, followed the tutorial exactly and then suddenly started getting
`name: "StatusCodeError", statusCode: 500, message: "500 - undefined", error: undefined, options: Object, ...` error

I have a key pair and the way I generate invoices is the exact same as is in the tutorial, except now instead of printing out invoice related information it just gives me this. I'd provide my code, but it quite literally is identical to that of the example on the README. I tried generating a new keypair once or twice, but that didn't seem to change anything at all.