Google Sheets Script: Combining onEdit with openById("OtherSheetsId") - google-apps-script

Question

I am pretty bad at this but i did search around quite alot before posting here. I found some answers and I am now stuck at this part.
In short: We have 2 seperate google doc sheets. When a specific cell gets changed in Spreadsheet1, the script must change a specific cell's value in Spreadsheet2.
function onEdit(e) {
var mainsheet = SpreadsheetApp.getActive().getSheetByName('Main');
var changeit = sheet.getRange("A1").getValue();
var offsheet = SpreadsheetApp.openById("spreadsheet2s id").getSheetByName('Echo').getRange("A1");
if (changeit == 'true'){
offsheet.setValue('true');
}
It basically does not work, and in scripts, when I go to Run -> Executions Transcript it tells me Execution failed: You do not have permission to call SpreadsheetApp.openById.
When I try this for the same sheet it works fine.
It seems that an installable trigger would do the trick, but i have not been able to find anything on what exactly to do here, as in how to apply an installable trigger.
It is said by google info that this will allow a function to change info on another sheet. How would we make this only apply to the onEdit(e) function listed above?
And the biggest question is, how do we make this work / tie it all together? What I have done is just pasted this underneath (as if it was its own function).
I have played around with it in various ways (such as trying to add the openByID info in this and afew other silly things) and I think I missing something simple here.
function createSpreadsheetEditTrigger() {
var ss = SpreadsheetApp.getActive();
ScriptApp.newTrigger('onEdit')
.forSpreadsheet(ss)
.onEdit()
.create();
}
Thank you in advance for your help.

Answer 1

Try this:
function ss1OnEdit(e){
if(e.range.getSheet().getName()!='Main') return;
SpreadsheetApp.openById("ss2id").getSheetByName("Echo").getRange(e.range.getA1Notation()).setValue(e.value);
}
//You can run this function all you want it will not create more than one trigger. But you must run it once to setup the first trigger.
function createSS1OnEditTrigger() {
var ss=SpreadsheetApp.getActive();
var trgs=ScriptApp.getProjectTriggers();
var found=false;
for(var i=0;i<trgs.length;i++) {
if(trgs[i].getHandlerFunction()=="ss1OnEdit") {
return;
}
}
if(!found) {
ScriptApp.newTrigger("ss1OnEdit").forSpreadsheet(ss.getId()).onEdit().create();
}
}