Hello,
If you need a quick look at Jira's API answer straight from a ticket in your web browser, I suggest you to use a bookmarklet.
A bookmarklet is managed as a regular booklet, but lets you run a javascript command on your current page. In our case :
javascript:location.href='https://{your_company}.atlassian.net/rest/api/2/issue/'+document.location.href.split('/')[4];
It just extracts the ticket reference ({projectId}-{ticketNumber}) out of the current web URL. Then it calls the API with the relevant parameters.
Personnally I use this bookmarklet to retrieve the internal id.
HTH
Nicolas Gondard