Business Rules - Validation Salary with Warning (promote and change position)

Summary:

Problems with alert not appearing at the right time

Content (please ensure you mask any confidential information):

Hi, on the promote and change position page, in the salary section, I need an alert to appear if the salary is higher than the position's budget. The problem is that the alert only appears when I click on continue to the next section or submit and return to the salary section again, how do I make it appear immediately when I enter a salary value greater than the budget? For the alert to appear at run time as soon as I enter a higher salary?