In most cases, a manifest is ‘Rejected’ because it was submitted too late. Customs only allows manifests to be submitted electronically no later than 9 days after departure. If this is the case, you can request Customs to still register the rejected notification. Sending the manifest again is not needed. When Customs registers the manifest, the status in the service will change to ‘Accepted’.
In other cases, you can contact the service desk.