java.sql.SQLException: near "on": problema de error de sintaxis

En Sqlite 3.6.0, quiero actualizar el registro si existe o insertarlo, pero recibo un error como

java.sql.SQLException: near "on": syntax error

mi consulta sql de la siguiente manera;

INSERT INTO tx (
               _id,
               amount,
               fee,
               prev_hash,
               nonce,
               action_time,
               completion_time,
               _from,
               _to,
               asset,
               hash,
               block,
               seq,
               [desc]
           )
           VALUES (
               ?,
               ?,
               ?,
               ?,
               ?,
               ?,
               ?,
               ?,
               ?,
               ?,
               ?,
               ?,
               ?,
               ?
           )
           ON CONFLICT (
               _id
           )
           DO UPDATE SET amount = 1.0,
           fee = 0.001,
           prev_hash = 'e6d0ca4b71488972cb149eef427ffbeb6132449c045c88db89ddaa8ab0c3611f',
           nonce = 1544773280,
           action_time = 1544773276808,
           completion_time = 1544773276808,
           _from = 'SKK1P5eQqoN7FBKnughbvp3UBK2CyjRQhHBp',
           _to = 'SKK1KuAwe4kR1SfdoXDiQStVtRPvdTVaKy2ry',
           asset = 'SKK',
           hash = '',
           block = 100,
           seq = 15288,
           [desc] = 'denemee'

Y mi código se bloquea como sigue;

sql = "insert into tx (_id,amount,fee,prev_hash,nonce,action_time,completion_time,_from,_to,asset,hash,block,seq,desc) "
                                    + "values (?,?,?,?,?,?,?,?,?,?,?,?,?,?) on conflict (_id) do update set "
                                    + "amount =" + tx.amount + ",fee=" + tx.fee + ",prev_hash='" + tx.prev_hash
                                    + "'" + ",nonce=" + tx.nonce + ",action_time=" + tx.action_time
                                    + ",completion_time=" + tx.action_time + ",_from='" + tx.wallet + "'" + ",_to='"
                                    + tx.to + "'" + ",asset='" + tx.asset + "'" + ",hash=''" + ",block=100"
                                    + ",seq=" + tx.seq + ",desc='" + tx.desc + "'";
                            PreparedStatement pstmt = con.prepareStatement(sql);
                            pstmt.setString(1, tx._id);
                            pstmt.setString(2, String.valueOf(tx.amount));
                            pstmt.setString(3, String.valueOf(tx.fee));// fee
                            pstmt.setString(4, tx.prev_hash);// prev_hash
                            pstmt.setString(5, tx.nonce);// nonce
                            pstmt.setString(6, String.valueOf(tx.action_time));// action time
                            pstmt.setString(7, "");// completion_time
                            pstmt.setString(8, tx.wallet);// from
                            pstmt.setString(9, tx.to); // to
                            pstmt.setString(10, tx.asset);// asset
                            pstmt.setString(11, tx.hash);// hash
                            pstmt.setString(12, "");// block
                            pstmt.setInt(13, tx.seq);// seq
                            pstmt.setString(14, tx.desc);// desc
                            pstmt.executeUpdate();

la consulta en bruto funciona en sqlitestudio con éxito, pero recibo un error. Sé que sqlite versión 3.6.0 admite eventos upsert. ¿Dónde lo estoy haciendo mal? ¿Cómo puedo manejar este problema correctamente?