Can’t add more than 3 digits for customer credit

Hi, I can’t type more then 3 digits when I try to add customer credit amount.

I click to adjust credit, then a popup shows to add credit, and if I try to type any number that bigger than 999 the script freeze, can not type the 4th digit, or send form, or close popup.

I also tried to copy 4 digit number, and paste to the form, it freeze immediately if copied the 4 digit number

Any solution?