I have an App Router API route (app/api/diagnose/route.ts) that POSTs multipart/form-data to PlantNet. I only append:

images (as Blobs from fetched URLs)

organs=leaf

Yet PlantNet returns:
{"statusCode":400,"error":"Bad Request","message":""lang" is not allowed","validation":{"source":"payload","keys":["lang"]}}

Repo grep shows no lang anywhere. Using Next.js 15 (dev), Node 20.

Questions:

Any chance Next/fetch/FormData is adding lang implicitly?

Best way to inspect/dump the exact multipart body an API route sends?

Thanks!