Communication with buyers or other sellers should be professional and polite. If you are discussing about a project and unintentionally use any of the words like payment, fees, or any payment methods, it will get flagged but when fiverr team will review it, nothing should happen. I told this from my own experience where I was working for an escrow client. We had to discuss various aspects of payment methods etc for creating a white paper. Sometimes the messages got flagged but when they reviewed the messages, it was fine. By no way, you should disclose any personal details like phone numbers, email id or any other ways to be able to communicate outside of fiverr. That will create a serious trouble for you.