"I have two hands and two feet."
Translation:Ich habe zwei Hände und zwei Füße.
1) ß is not a B
2) Both the app and the website allow you to choose the character. (With IOS, for instance, press the key longer on the phone and then choose the right letter.)
3) ss instead of ß is accepted, but a single s isn't. Rightfully so.
4) Agree, DL is sometimes inconsistent. That is why users can report errors and thus improve the courses.