The gas fee was sufficient and there were no other suspicious causes.
However, there was an issue in which a transaction cannot be made due to a long time pending after requesting more than a certain number of requests.
please check this issue.
Thank you dear infura team.
Hi @ben.choi, when you’re sending that many transactions at a time if one transaction gets stuck (doesn’t get mined in time, etc.), the others will remain stuck as well. I would suggest putting in a slight pause after each transaction to ensure each one gets mined before the next ones move forward.
Thank you for helping me dear Leiya.
So, a node(the api that I call using an api key) works in a way of queue. does it? 
Hi @ben.choi - yup! Basically, your transactions need to get mined in the order in which they were sent, or you run the risk of one txn not getting mined for whatever reason and holding up the rest of them. When you send the txns, you assign a nonce, which determines the order in which they get mined. So, if your transaction with nonce 6 has too low of a gas price to get mined (for example), that will keep any nonces after number 6 from getting mined as well.