Quote created. Returns the full fetch-shape payload for the new
draft. On create, sections, content_blocks, attachments,
custom_fields.*, totals, billing_address, and
shipping_address are empty — sections and line items are
added via their own endpoints.

Malformed request body (unparseable JSON).

Validation failure. Every problem found in the request is
reported together in a single errors array rather than one
per response.

Includes ERR_NO_CLIENT_IDENTIFIER when neither client_id nor
client_name is provided, invalid expired_at, currency_iso
mismatch, a malformed contact.email
(ERR_CONTACT_EMAIL_INVALID) or owner.email
(ERR_OWNER_EMAIL_INVALID), and — when owner.email is
supplied — an email that was not found
(ERR_OWNER_EMAIL_NOT_FOUND).

References that are not found are reported here too:
ERR_TEMPLATE_NOT_FOUND for template_id,
ERR_CLIENT_NOT_FOUND for client_id or client_name, and
ERR_CONTACT_NOT_FOUND for contact.email.