Using delivered order files for my demo


I am a voice over talent. Am I able to use a file from a delivered order, without permission from the buyer, to update my demo, or do I need to get permission from the buyer first?


i contacted to fiverr CS and they advice me to get permission from buyer first.
Also some seller offer gig to buyer with,
“By ordering this gig you agree that I retain the right to display the final delivery in my demo/online portfolios and promotional materials”