。
Thanks so much.
Literal
Truly somehow.
どうも is an extraordinarily versatile conversational filler — by itself it can mean 'thanks,' 'sorry,' 'hello,' 'very,' or 'somehow,' depending on context and intonation. Here it's a casual 'thanks' with 本当に intensifying the sincerity. Literally どうも means 'in what way,' but the word has drifted into a fixed polite marker for various social situations. No verb is present — this is a fragmentary expression.