Google Sheets Android insert function

In Sheets, I get a parse error.
What is my error?
Be kind. Totally new at this.
This version doesn’t support getactivespreadsheet maybe?
I paste exactly this into a cell:

=sheetName()
function sheetName() {
var ss = SpreadsheetApp.getActiveSpreadsheet();
var sheet = ss.getActiveSheet();
return sheet.getName();
}