When you get status of an envelope through REST, voidedReason
is one of the responses.
https://demo.docusign.net/restapi/v2/account/{accountId}/envelopes/{envelopeId}
status:"voided",
..
voidedDateTime:"2014-02-02T11:37:18.5500000Z",
voidedReason:"Envelope has expired."
When an envelope has expired, it will show: "Envelope has expired."
When someone declines or cancels an envelope, it will show the comments they entered in the text box upon voiding.
These responses given above do not show unless the envelope is in a voided status, so you'll want your request to only use this information is status is equal to 'voided'