Melbet's "Tennis Acca Insurance" feature is designed to give bettors added security on their accumulator (acca) bets, specifically in tennis. When customers place an accumulator bet on multiple tennis matches, this feature allows them to receive a refund on their stake if one selection loses, provided they have included a minimum number of selections in their bet (usually three). The refunded amount is typically credited as a bonus or free bet, allowing users to continue betting without a total loss. This feature enhances the betting experience by mitigating the risks associated with accumulator betting, especially in a sport where upsets can occasionally occur.