Powershell script not recognizing my function

Powershell processes in order (top-down) so the function definition needs to be before the function call:

function email($text){
    #email $text
}

#Do things | 
foreach{
    email($_)
}

It probably works fine in the ISE because you have the function definition in memory still from a prior run or test.

When it comes to the Function-Calls, PowerShell is fairly different from other programming-languages in the following ways:

1. When passing the arguments to a function, parentheses are NOT allowed (and will raise a parse error if Set-StrictMode is set to -version 2.0 or above/Latest), however, Parenthesised arguments must be used to call a method, which can either be a .NET method or a user defined method (defined within a Class - in PS 5.0 or above).

2. Parameters are space-separated and not comma separated.

3. Be careful in where you define the function. As PowerShell sequentially processes line-by-line in top-down order, hence the function must be defied before that function is called:

       Function func($para1){
             #do something
       }
       func "arg1"  #function-call
   

In Windows PowerShell ISE (or Visual Studio Code) if a function-call appears to be working even though the function-definition is defined below the function-call, (beware) this is because it's cached in memory from a previous execution(s), which too will fail as soon as you update the function-definition.