Correct issue in a "home made" Chrome extension script

I have a very annoying issue on a "home made" Chrome extension.

This extension is supposed to input a value in an input field, for example 20. But when submitting the form, the value changes to 1 clicking on "submit".

I need to correct this. Work will have to be done through teamviewer as the website only authorizes specific IPs to login.

Thanks.