data envelope; authentication endpoints return the token object directly; errors use an error envelope.
Single resource
Collection
Lists return an array underdata.
Token (authentication)
POST /v1/oauth/token and the login endpoints return the token object without a data wrapper:
Empty
Some actions (e.g. revoking an API key) return204 No Content with an empty body.
Error
Amounts & timestamps
Monetary amounts are integers in minor units (cents). Timestamps are ISO 8601 strings in UTC.