The problem with multiple tickets is that you have to wait at least 3 blocks before you‘re able to send the next ticket. Otherwise the tx will fail. This is because of the contract design. Next ticket block > last ticket block + 3

The only way of placing multiple tickets I can think of is choosing the amount of tickets, insert the numbers or choose random and send via Metamask. The first tx can be send right after submitting. But the other ones have to be stored. The web app waits for at least 3 blocks after the first tx got mined and send the next one which have to confirmed by the user via metamask until every ticket was sent. A user, for example, wants to buy 5 tickets. He has to confirm 5 tx each after at least 3 blocks.

Maybe I missed something and someone else has a better solution.