The submit button is grayed out when Agents try to submit a request.
You are not a light agent trying to make a public comment.
There are different causes for the submit button being grayed out. Often times this issue is experienced while using the Project app. The Project app will not allow an agent to solve a ticket until all child tickets are solved out. To test this functionality and ensure the issue is related to the apps, you can add ?noapps to the end of your URL. Doing so will disable all of the apps in the account.