The error message is giving you a clue, when you call the function you are passing two arguments (i.e. n and seed) but, you haven't defined this arguments in your function and also you are not using them in your code, so you have to check the code for your function again to make sure it does what is supposed to do.
For example, here I'm defining the sample_function() function which takes two arguments (a and b) and returns the sum of both numbers.
sample_function <- function(a, b) {
a + b
}
sample_function(a = 2, b = 5)
#> [1] 7
Created on 2019-09-30 by the reprex package (v0.3.0.9000)