I think you have to customize your service activity to do this validation. You need to check field value class with the value of pyStatusWork coming from the external system to ensure it is present.

So, basically you want to check , whether the status coming from service activity is already present in system or not.

For example, if the status is Pending-Business you want to cross check whether such status are present in the system or not.

For that, I guess , you need to first have a placeholder for all the status that you have in your system. 

Browsing thru all the field value everytime might cause a performance overhead. So , instead , if you store them in a table and then refer that via your service activity , then it might reduce the complexity.