[2023] Trying to add a NEW character to my jagex account

I linked 3 characters to my jagex account just last week. I’m looking to create an Ironman on RS3, and every time I try to make a new character it’s requiring me to make a new account first (with a new email). Am I missing something? Is there a way to login to my jagex account and just create a new character? Or do I really need to make a new email to create an account to then merge it with my jagex account? What’s even the point of having your characters under one account if you still need a new email for every character

Appreciate the help in advance. Somewhat of a returning player here