Get a branded chain from the likes of KMC, SRAM, Shimano etc, can be silver finish, black or even colour. As it's a hub gear bike you need a 1/8" chain, not 3/32" or 8/9 speed which are derailleur types.
Due to the rear of seat tube battery making the bike longer, many standard bike chains are not long enough, so check the number of links you need. As a short cut to buying correctly
50cycles stock spare ones usually.