Why is my calculated signature different from what is expected?

Please review that the "payload" value in the notification maintains the same structure or order originally offered. The provided calculated signature will be different if the order is changed. For example,

var payload = '[{"updatedAt":"2018-05-06T20:11:34.421Z","humanId":"g37150614be22d72fd9101e418df16dd","endpoint":"https://api.humanapi.co/v1/human/activities/summaries","type":"activitysummary","model":"activitysummary","action":"updated","objectId":"3a9e4107cc6a0c0500e3afb8"}]'

is not equivalent to

var payload = '[{"objectId":"3a9e4107cc6a0c0500e3afb8", "updatedAt":"2018-05-06T20:11:34.421Z","humanId":"g37150614be22d72fd9101e418df16dd","endpoint":"https://api.humanapi.co/v1/human/activities/summaries","type":"activitysummary","model":"activitysummary","action":"updated"}]'