Bitcoin RPC getbalance of address I sent coins to on regtest
getbalance returns the balance of an account, not an address.  https://en.bitcoin.it/wiki/Original_Bitcoin_client/API_calls_list

If there's no account by the name of mvt7M16caMH1xoJyfWU5orjArfq97jhZ7k, it will return 0.

Try using getreceivedbyaddress instead.