Square has expanded its Bitcoin payment acceptance network to US merchants. The approximately 4 million merchants represent its merchant network, not the number of stores already accepting BTC. The rules are listed on the help page: It uses the Lightning Network, with default settlement in USD; the single transaction limit is approximately $600, and the daily limit is $20,000; disputes and chargebacks are not supported, and refunds are issued in Square e-gift cards; it is not available in New York State. Merchants can already accept Bitcoin payments. But how many customers actually have a Lightning wallet on their phones?