Thank you for your response while you are busy.

I have the grant type set to "JWT Bearer".

The reason is that to use the service account key as authentication information, I attached the JSON file as a certificate and generated JWT because it was described in the following article, so I executed it.

https://community.servicenow.com/community?id=community_article&sys_id=506d94d01b1ddc1017d162c4bd4bc...

So, I would like to set the grant type to JWT Bearer, but is it not possible or not to generate a refresh token with this method?

Thank you!