Short answer
No, daily mandarin slices are not recommended. While a small piece of the flesh occasionally is okay, regular feeding can cause stomach upset or diarrhea due to the sugar and acid. Offer it only as a rare treat, and if you see vomiting, diarrhea, or loss of appetite, stop and contact your vet.
Mandarin — Food safety facts
Feed with care · Dogs · full breakdown on the linked food page
A small segment of flesh is usually tolerated; peel and seeds are not.
The full verdict, portion guidance and serving notes are collected on the Mandarin food facts page.