Ambiguous use of 'str' error

Hello everyone. I started looking at Chris’ tutorial on youtube (iOS Tutorial (2020): How To Make Your First App), and I am stuck on Lesson 5. I am getting this “Ambiguous use of ‘str’” error, and I’m not sure why. This happens every time I enter “let str = “more data”” ! I uploaded a photo. Can someone please help me? Thanks!

You declared str as a variable on line 4 and the try to redfine it as a constant on line 9. You can’t do that. Pick a different name for one of them.