This organization isn’t authorized to upload change sets to other organizations. For authorization, contact the deployment connections administrators on the organizations where you want to upload changes.

This error is coming, just because of deployment settings. Seems like you have not created deployment connection between your source org and destination org.

To create deployment connection log into the destination org and follow below steps.

Setup -> Deploy -> Deployment Setting -> Select source sandbox from the available list of sandboxes – Edit -> Check allow inbound change sets check box and save.