How to make a pop-up (app.response) where u can only fill in numbers?

You can't force them to only enter numbers. You can, however, validate what they entered and if it's invalid display an error message and stop the script from executing further.

Something like this:

if (cRTN==null || /^\d+$/.test(cRTN)==false) {
	app.alert("Invalid value.");
} else {
	// rest of code goes here
}

Hi Niels.

You can go into the field properties (select Prepare Form from the Tools menu) and change the filed's Format to "Number".  Similar to Excel you can, set the number of decimal places, seperator style, currency symbols, etc. and set the paramaters to your liking.

 I use this feature pretty often when creating forms for my department. Hope that helps! 😊