C# SQlite SQL logic error or missing database\r\nnear \"a\": syntax error

I get an error when I try to run this method:

public bool InsertLog(string logMsg, string type)
{
    bool result = false;

    string sql = "INSERT INTO `log`(`logmsg`, `type`) VALUES (?a, ?b)";


    using (SQLiteConnection conn = new SQLiteConnection(m_dbConnectionString))
    {
        conn.Open();
        using (var comm = conn.CreateCommand())
        {
            comm.CommandText = sql;
            comm.Parameters.AddWithValue("?a", logMsg);
            comm.Parameters.AddWithValue("?b", type);
            int res = comm.ExecuteNonQuery();
            result = (res == 1);

        }
        conn.Close();
    }
    return result;
}

On this database table:

CREATE TABLE log (
    id        INTEGER  PRIMARY KEY,
    createdAt DATETIME DEFAULT (datetime('now', 'localtime') ),
    logmsg    TEXT,
    type      VARCHAR
);

The error message is {"SQL logic error or missing database\r\nnear \"a\": syntax error"} (System.Data.SQLite.SQLiteExpcetion). Where is the syntax error in the insert query? I don't see it. Can't I use prepared statements this way?