Only allow numbers in textbox

Where are you adding the code? What type of question are you using? How many Text Entry Boxes are there?

Qualtrics.SurveyEngine.addOnload(function()
{
this.getQuestionContainer().querySelector(".TextEntryBox").type = "Number";
});
And I use a text entry question. I guess that's the problem?
It's just text and respondents are supposed to enter a number in the text box below

Hi FloNeb
I believe Validation Type--> Number as a Content Type option should have worked. However, just wanted to share that text box will allow you to enter the any text and once you click the next/submit button than the validation will happen and show the error message. If this does not fit your requirement than you need to use the custom code to alert the respondent on mouse up after validating each keystrokes.