apiKey header. Create a public key (ntpub_…) in the Niva dashboard under Settings › API Keys. A private key is rejected with 401.{submission_token} in the path with the submission's token, returned by Create new submission or Get submission. Retrieve it on your server with a private key and pass it only to the applicant who should access that submission. It expires 24 hours after issue; call Get submission for a fresh token.401 with {"errors": ["401 Unauthorized"]}: the apiKey header is missing, invalid, or not a public key.401 with {"errors": ["Invalid token."]}: the submission token is malformed or expired.404 with {"errors": ["Record not found."]}: the submission belongs to another account, or the document is not available in this submission.