The current Request webhook doesn't seem to include the Request Cancellation reason. Currently it just says:

'event' => {
'desc' => 'Request canceled',
'value' => 'REQUEST_CANCELED'
},

The comment field refers to the request, but not the cancellation reason here:

'userrequest' => {
'requesttime' => '2022-05-11T23:42:26.191Z',
'managedbycirculationdeskcode' => 'EASTCIRC',
'mmsid' => '993815723607636',
'taskname' => 'Rejected',
'author' => 'Ferguson, J.',
'itemid' => '2365452260007636',
'issue' => '',
'pickuplocationlibrary' => 'ABC',
'dateofpublication' => '',
'managedbylibrary' => 'State Library',
'requesttype' => 'HOLD',
'requestid' => '1419991190007636',
'pickuplocation' => 'Redmond Barry Reading Room',
'materialtype' => {
'desc' => 'Book',
'value' => 'BOOK'
},
'requestsubtype' => {
'desc' => 'Patron physical item request',
'value' => 'PATRONPHYSICAL'
},
'volume' => '',
'managedbylibrarycode' => 'ABC',
'part' => '',
'barcode' => '30328504468884',
'expirydate' => '2022-05-19Z',
'description' => undef,
'pickuplocationtype' => 'CIRCULATIONDESK',
'comment' => undef,
'userprimaryid' => '12345678',
'pickuplocationcirculationdesk' => 'DEFAULTCIRCDESK',
'managedbycirculationdesk' => 'East Retrieval',
'requeststatus' => 'HISTORY',
'title' => 'Life.',
'requestdate' => '2022-05-12Z',
'additional_id' => '141-999-119'
}