So I have the following code for when the \"Add player\" button is clicked
private void addPlayerBtn_Click_1(object sender, EventArgs e) { //Do some code
When you call a function, you provide actual arguments, which are values, not formal arguments, which are types and parameter names.
Change
addPlayerBtn_Click_1(object sender, EventArgs e);
to
addPlayerBtn_Click_1(addPlayerBtn, EventArgs.Empty);