Calculation Output Validation String

Hi community, I am building a form through excel, form is working fine but I have created a matrix question where the third column has a simple subtraction calculation of previous two columns. I want to highlight the output value if it comes <0 with an error message. But despite of trying so many validation syntaxes, failed to get the desired output. Please help. The screenshot of the excel form, is attached.

Welcome to the community, @magarwal! Maybe this support article we have should help you solve your issue: