When I was trying to send multiple transactions, I received an error saying that "replacement transaction underpriced".
Searched around and it says that I was trying to replace an existing transaction, so I need to pay a higher price. But that was not my intention.
Searched further and it says that I need to increase the nonce or use a different nounce.
The question now is, can I use a random number? (just assume this random number will not repeat in the next one day)