'In the 2015 parliamentary elections, 176,491 people, 30.5% of all participants, voted over the Internet.'
https://en.wikipedia.org/wiki/Electronic_voting_in_Estonia#2...
Tom Scott on electronic voting: https://www.youtube.com/watch?v=w3_0x6oaDmI
How do you know that it was successful? I'd say that, in order to be successful, an election must ensure that (1) the votes are accurately counted and (2) the voters aren't bribed or coerced w.r.t. their votes. Traditional voting at polling places ensure this by having voters mark their ballots in secret and keeping the paper ballots available for a recount. I don't see how it is possible to provide either ballot accuracy or ballot secrecy if voters can vote on insecure (possibly malware-infected) computers in an uncontrolled physical location (possibly being watched by someone bribing or coercing them to vote a certain way).