You can use regular expression to check whether input string is number or not.
In addition, based on your workflow, even if one value is not a numeric, you are asking user to enter both the values. But in a standard solution, you don’t need to proceed further until the first value is valid.
Just keeping it simple, you will want to check if it’s Numeric before checking if it’s less than 0
The condition can be like this:
If(IsNumeric(sNumberOne) And IsNumeric(sNumberTwo), CInt(sNumberOne)<0 And CInt(sNumberTwo)<0, True)
So if you place that entire line into your condition, it will first check if both values are numeric, then check if they are <0. If they are not numeric it will go to the True side. Basically, I used an inline If statement, useful for making comparisons that need to be a certain type before making.
I liked your solution above the others because it was a very simple approach. Also thanks for your explanation and indeed, it seems to work with your tips. Nevertheless, I found a new solution that I will put here just in case for future knowledge sharing: