Lychee — Food safety facts
Feed with care · Dogs · full breakdown on the linked food page
Flesh only, and only a little — it is very high in sugar. The pit is a choking and obstruction hazard.
Short answer
Watch for signs of digestive upset and ensure he didn't swallow any pit. The flesh of lychee is safe in tiny amounts, but it's extremely high in sugar, which can cause diarrhea, gas, or an upset stomach in a puppy. The much greater danger is the pit, which is a choking hazard and can cause a life-threatening intestinal blockage. Since you peeled them, the immediate pit risk is lower. Monitor your puppy for vomiting, loss of appetite, or any straining to poop over the next day, and call your vet if you see concerning signs.