An FBR notice in your IRIS inbox is not a disaster, but ignoring it can become one. Most notices are routine: a return not filed, a mismatch in declared data, or a request for records. The response, not the notice, decides how the matter ends.
The golden rules are simple: never ignore a notice, always respond within the stated time, respond through proper channels with documentary evidence, and get professional help before replying if the amounts or the language are serious. A weak first reply can lock you into a bad position for the rest of the proceedings.