u/Firm_Ask2717

I work for a small media agency, and I am currently assigned as the manager of a client's account. Recently, my company would like to start our own newsletter. How can I add to our account without opening a brand new account and also not affect our client's account? I've read all the support articles about combining multiple accounts, but I believe we are currently on the free plan and our client is on the premium one, and I cannot figure out how to upgrade OUR plan. Does my boss just need to call and figure it out through sales, or am I missing a simple solution?