Stringify an object

I need to send an invoice to a client. Convert the invoice object with id 2026-0817, amount 425.5, currency USD, lineItems as an array into a JSON string and include it in the HTTP POST body to billing.example.com/invoices, then log the request body and the server response.

Before I include this payload in the billing request, make the stringified JSON more reviewable: ensure numeric amounts keep two decimals, move metadata to a top-level metadata object, and show the final string with keys sorted so a reviewer can spot price or currency mistakes quickly.

I tried POSTing a new invoice and the API returned 415 Unsupported Media Type; the code uses JSON.stringify but the server still complains. I’m not sure if I missed headers, included circular refs, or accidentally sent an object wrapper. What’s the most likely oversight and the minimal fix to get a valid request out now?

We keep getting billing errors because different clients send semantically similar invoice objects in different shapes. Each time I patch one client’s serializer. Which serialization habit should I standardize across the codebase to reduce these incidents, and what small validation or lint rule would stop the most common mistakes before they reach billing?