What did I do wrong on this script? It says "Cannot find function createMenu in object Spreadsheet."

Question

What did I do wrong?

function onInstall() {
    onOpen();
function onOpen(e) {
    SpreadsheetApp.getActive()
        .createMenu('Sentrix Messaging')
        .addItem('Index', 'new mail')
        .addItem('Compose', 'Write mail')
        .addToUi();
    Browser.msgBox('Welcome to Sentrix Email');
    ShowSidebar();
}

function showSidebar() {
    var html = HtmlService.createTemplateFromFile("Inbox")
        .evaluate()
        .setTitle("Email");
    SpreadsheetApp.getUi().showSidebar(html);
}
}

It says

Cannot find function createMenu in object Spreadsheet

Answer 1

I think you made a mistake with brackets.

function onInstall() {
    onOpen();
}
function onOpen(e) {
    SpreadsheetApp.getActive()
        .createMenu('Sentrix Messaging')
        .addItem('Index', 'new mail')
        .addItem('Compose', 'Write mail')
        .addToUi();
    Browser.msgBox('Welcome to Sentrix Email');
    ShowSidebar();
}

function showSidebar() {
    var html = HtmlService.createTemplateFromFile("Inbox")
        .evaluate()
        .setTitle("Email");
    SpreadsheetApp.getUi().showSidebar(html);
}