after flexi task action add run-if action to check if task outcome was REJECTED.

add send notification action into run-if action and configure your notification message.

Hello,

I would just include a send email action on the Reject branch of the flexitask - assuming its a list workflow set the To field of the send email to the Initiator (person who starts the workflow) - as long as your workflow is set to run on item create, initiator will be the person who submits the form (unless you customize something else).  

Thanks,
Mike

Did either of our suggestions solve your issue?  If so please mark the answer that helped you as correct.  Thanks

I've followed these instructions (added Email Notif after REJECT as well as a RunIf with a email notification)  NO notification is received (not in junk either). WF is set to run on Create. Please Advise

update to RunIf config - still NOT getting emails