acc = db.GetCollection<AccountModel>("accounts");

accs = db.getCollection("accounts", AccountModel.class);

public void InsertPlayer(String username){

    Model_Account newAccount = new Model_Account();
    newAccount.Username = "username";
    newAccount.Password = "password";
    newAccount.Email = "email@hotmail.com";

    accounts.insertOne(newAccount);

}

Caused by:org.bson.codecs.configuration.CodecConfigurationException: Can't find a codec for class AccountModel.