...no dress code. Business casual, jeans and polo style shirts, T-shirts, suit and tie, tennis shoes, loafers, it's all OK. Dress appropriately for where you are going to see her and what you will be doing. (if it's a dinner, lunch or night out date.) It's been discussed before and many of the responding providers did say they had a preference but no deal breakers.
The deal breakers in regard to how you are dressed is if the clothes are not neat, clean, and appropriate for the situation. EX: It would not be good to show up in raggedy jeans, old t-shirt and worn out tennis shoes to go in a nice hotel to see her.
I have worn slacks, polo shirts, loafers to 90% of my sessions. I have occasionally worn jeans. Once or twice I wore a sport coat with a dress shirt, slacks and dress shoes, no tie. A few times it was a t-shirt and jeans and nice, clean, in good condition tennis shoes. Never was there an issue with it.
Look at the link below. It is a discussion on this topic. Do a search and I'm sure you can find more of these discussions. The point is be completely clean, neat, and dressed to fit in where the appointment will take place.