Selected cell does not update when using button linked to script

I have a sheet for users to enter a cash-count and their initials then hit a button which runs a script and stores these inputs in a table.

The problem is, if the user types the information (e.g. their initials) and hits the button without first pressing Return or selecting another cell, the information is not saved.

I've seen a similar post: How to force flush a user's input? and tried the solutions, some don't work and none are really what I'm looking for. I know that I could use a Checkbox instead of a button but I'd like to find a way do it without resorting to that. The table is a cash-count for a till so not all cells require a value (there may be no $100 notes for example) and I won't know which was the last cell edited.

[The Data][1] [1]: https://i.sstatic.net/mdKXk.png

The Code:

function Accept() { 
  var ss = SpreadsheetApp.getActive();
  var sheet = ss.getActiveSheet();
  var db = SpreadsheetApp.getActiveSpreadsheet().getSheetByName("DATA");
  var vals = db.getRange("B:B").getValues();
  var last = vals.filter(String).length;
  var ui = SpreadsheetApp.getUi();
  var user = ui.prompt("Notes:");
  var values = [[
      sheet.getRange("I7").getValue(),    //Date/Time
      sheet.getRange("N16").getValue(),   //Amount
      sheet.getRange("E17").getValue(),   //Initials
      user.getResponseText(),             //Notes
    ]];
  db.getRange(last+1,2,1,4).setValues(values);
}