It depends on the context and how it is done. Asking to move communication completely off the platform is usually a red flag because it goes against most platform rules. Platforms want all messages and agreements to stay within their system so they can protect both sides if something goes wrong. Some platforms allow sharing contact details after a contract has started, but doing it before a contract is in place can get your account flagged or even suspended. The safest thing is to always communicate through the platform chat until the rules clearly say otherwise. Have you ever been warned for this?