Mac Desktop App Malicious Software Error

We have a developer that has put together a Mac application for us but we are getting an error message that he says he can't resolve because it has something to do with Mac. I have found steps on how to fix the situation one at a time, but this application is being rolled out to thousands of computers and we need this to be resolved permanently upon installation rather than every user having to take manual steps to resolve it. Image of the error is attached. We can do hourly or fixed price, whatever makes the most sense to you. We just need this resolved ASAP.