The full error catalog

Every code /v1 emits, with its HTTP status and what to do. They are stable: from the first integrator they are NOT renamed (that would break your switch). English only, on purpose (the code is the contract, the message is for pasting into a log and googling).

code	HTTP	message	action
API_KEY_MISSING	401	The Authorization header is missing or malformed	Bug in your integration — send Authorization: Bearer wc_live_…
API_KEY_INVALID	401	The API key is invalid or has been revoked	Check / rotate the key in the panel
ACCOUNT_SUSPENDED	403	Account is suspended or cancelled	Resolve billing / contact support
RATE_LIMITED	429	Per-key rate limit exceeded	Back off and retry (limit 600/min per key)
IDEMPOTENCY_KEY_REQUIRED	400	The Idempotency-Key header is required	Send a unique UUID in Idempotency-Key
INVALID_TYPE	400	type must be text, template, image, document, audio or video	Fix type
INVALID_BODY	400	text.body (or template.name) is required	Fix the message body
INVALID_RECIPIENT	400	to must be a plausible E.164 number (8–15 digits)	Fix to
MEDIA_LINK_OR_ID_REQUIRED	400	A <type>.link (https URL) or <type>.id (Meta media id) is required	Send one of them under the media object
MEDIA_LINK_AND_ID	400	Provide EITHER link or id, not both	Send only one
MEDIA_LINK_INVALID	400	<type>.link must be a well-formed https URL	Use a public https URL (Meta fetches it)
AUDIO_CAPTION_NOT_ALLOWED	400	type audio does not accept a caption	Remove audio.caption
CONNECTION_REQUIRED	400	Provide connectionId (conn_…) or from (phoneNumberId)	Send one of them
CONNECTION_NOT_FOUND	404	No connection matches connectionId/from for this account	Check the connection id (a number of ANOTHER account is also reported as not found)
CONNECTION_NOT_READY	409	The number exists but is not connected yet (details.status = its real state)	Wait for it to become connected, or refresh its status — do NOT change your payload
MESSAGE_NOT_FOUND	404	No message with that id for this account	Check the msg_… id
QUOTA_EXCEEDED	429	Plan message quota exceeded (policy block)	Upgrade plan or wait for the period to renew
MEDIA_ID_REQUIRED	400	A media id is required	Include the media id in the path
MEDIA_NOT_FOUND	404	No media with that id for this account (or expired at Meta)	Only fetch media ids from your own inbound events
MEDIA_TOO_LARGE	413	Media exceeds the size limit	Do not proxy files above the limit
MEDIA_UPSTREAM	502	Could not resolve/download the media from Meta	Retry; the media may have expired
INTERNAL	500	Internal server error	Retry; if it persists, contact support
APIKEY_NAME_REQUIRED	400	A non-empty name is required to create an API key	Send a name
APIKEY_NOT_FOUND	404	No API key with that id for this account	Check the key id
WEBHOOK_URL_REQUIRED	400	A url string is required	Send a url
WEBHOOK_URL_UNSAFE	400	URL must be https to a public host (private/loopback/link-local rejected)	Use a public https URL
WEBHOOK_EVENTS_INVALID	400	events must be known event types	Use the subscribable event types (see the event catalog)
WEBHOOK_NOT_FOUND	404	No webhook endpoint with that id for this account	Check the wh_… id
WEBHOOK_STATIC_HEADER_INVALID	400	The static header name is invalid or reserved	Use a valid header name; never Authorization/Cookie/Host/Content-*
WEBHOOK_CREATE_FAILED	500	Could not create the webhook endpoint	Retry
ALERT_NOT_FOUND	404	No alert with that id for this account	Check the alert id
CONNECTION_QUOTA_EXCEEDED	429	This number's monthly message limit is exhausted	Raise the limit for THIS connection (≠ upgrading the plan)
CONNECTION_EXTERNAL_ID_TAKEN	409	Another connection in this account already uses that externalId	Pick a different externalId (unique within an account)
CONNECTION_LIMIT_INVALID	400	monthlyMessageLimit must be a non-negative integer or null	Fix the value
INVALID_DATE	400	from/to must be YYYY-MM-DD	Fix the date
INVALID_PERIOD	400	period must be YYYY-MM	Fix the period
WEBHOOK_CONNECTION_INVALID	400	connectionId is not a valid connection id	Send a numeric connection id or omit for the account default
WEBHOOK_CONNECTION_NOT_FOUND	404	No connection with that id for this account	Check the connection id
ONBOARDING_MODE_INVALID	400	mode must be cloud_api, coexistence, or omitted	Fix mode
ONBOARDING_RETURN_ORIGIN_INVALID	400	returnOrigin must be an exact https origin (public, no path)	Send https://host (SSRF-guarded)
ONBOARDING_REDIRECT_URL_INVALID	400	redirectUrl must be a public https URL	Send an https URL (SSRF-guarded)
ONBOARDING_LINK_NOT_FOUND	404	No onboarding link with that id	Check the onb_… id
ONBOARDING_LINK_INVALID	404	This onboarding link is not valid	The token is wrong/unknown
ONBOARDING_LINK_USED	410	The link was already used	Issue a new link
ONBOARDING_LINK_EXPIRED	410	The link expired	Issue a new link
ONBOARDING_LINK_REVOKED	410	The link was revoked	Issue a new link
ONBOARDING_LINK_ALREADY_USED	410	This onboarding link was already used	Issue a new link (single use)
BRAND_LOGO_URL_INVALID	400	brandLogoUrl must be a public https URL	Use a public https image URL (SSRF-guarded)
BRAND_COLOR_INVALID	400	brandColor must be a #RRGGBB hex color	Fix the color
BRAND_EMAIL_INVALID	400	brandSupportEmail must be a valid email	Fix the email
BRAND_WEBSITE_INVALID	400	brandWebsite must be an https URL	Fix the URL