Hi,

Well, I'm very grateful that you sent an invitation to work on your project. I read your description and it's a fun project but unfortunately, the thing is that projects like this are fun to do but on the other hand very time-consuming and require a lot of hard work so I prefer to do these projects on a one-on-one basis just to avoid competition and save my energy. I hope you can understand.
There are really skilled designers on the platform they might submit their designs to your project but so sorry I'll have to decline your invitation. But if you still want me to work on this project you can always hire me on one on one basis.

So sorry for any inconvenience that I may have caused you.

Best of luck for this project.

Best regards,