I can´t receive twitts when a service is down but when the service is getting up the twitt is received..

I can´t receive twitts when a service is down but when the service is getting up the twitt is received..

can anyone help me?? i´m tryin to probe if the twitts are working, i changed the IP of my router inside the opmanager (i don't touch my router) to simulate a shutdown, the opmanager shows me the alert but any twitt is sending, but when i return the correct ip on the opmanager, i receive the twitt telling me the service now is OK.
 
what am i doing wrong??
 
regards