Every error is {"error": {"code", "message", "request_id"}}. Branch on code, not on the message, and quote request_id when you contact support.

Code	Status	Meaning
MISSING_API_KEY	401	No Authorization: Bearer header was sent
INVALID_API_KEY	401	The API key is not valid
API_KEY_EXPIRED	401	The API key has expired
CUSTOMER_SUSPENDED	403	The account is suspended
VALIDATION_ERROR	422	A required field is missing or has the wrong type; see details
RATE_LIMIT_EXCEEDED	429	Too many requests; wait Retry-After seconds
INVALID_REQUEST	400	The simulation service rejected the request, e.g. a bad version or file
SIMX_DECRYPT_FAILED	400	The .simx file could not be decrypted
SIMX_KEYS_UNAVAILABLE	502	The .simx decryption keys could not be loaded; retry later
FILE_UNREADABLE	400	The building file could not be read
PARAMETERS_INVALID	400	The simulatable-parameters document is not valid JSON or has no source.sha256
PARAMETERS_WRONG_BUILDING	400	The simulatable-parameters document was made from a different building
PARAMETERS_REJECTED	400	One or more changes cannot be applied; see message.problems
SIMULATION_REJECTED	400	The simulation engine rejected the file or settings, e.g. an unknown location
SXO_UNREADABLE	400	The uploaded file could not be read as a SIMIEN .sxo result
FILE_TOO_LARGE	413	The uploaded file is larger than the size limit
ALL_SIMULATIONS_FAILED	502	Every simulation in simulate-all failed
SIMULATION_TIMEOUT	504	The simulation engine did not respond in time; retry later
SIMULATION_SERVICE_UNAVAILABLE	502	The simulation engine is unavailable; retry later
UPSTREAM_UNAVAILABLE	502	The simulation service could not be reached; retry later
UPSTREAM_ERROR	502	The simulation service failed; retry later
UPSTREAM_AUTH_FAILED	502	The gateway could not authenticate with the simulation service; contact us
INTERNAL_ERROR	500	Unexpected error; contact us with the request_id