why I see this error regarding S9 L8 (Function Challenge)?

[JaSho145]

[prateek-aher]

That's what you got to figure out. That's the challenge. Close this issue please.

[JohnMeyerhoff]

I assume you missed the curly braces around your parameters which should not be there. it should be

add(int n1, int n2)

instead of

add({int n1, int n2})

Your optional Parameters are required in your method, this article might be helpful:
https://zaiste.net/posts/dart-optional-function-parameters/
The message you are getting does not get straight to the point because it does not see the issue in L16 of using them but rather in L15 because the optional parameters do not have a provided default value.
Please also refrain from sending large screenshots, as it will be sent to all 500+ people watching this repository by default.