403 Access denied! You don't have permissions for this page.

when I’m trying to submit a solution then error message arrived that is - 403

Access denied! You don’t have permissions for this page.
why I can’t submit the solution ???

If you are on a contest page which needs team registration, You need to make a team and login through the team id. For the currently running contest, any existing team won’t work and you have to make a new team and then login to be able to submit the solutions!