So you're asking me to explain why newton's third law is incorrect? I'm not a physicist and I definitely do not know tonnes of relativistic physics, do you expect me to? That's completely irrelevant response but cool, it's not a true statement because in some cases the momentum of an object is not conserved after applying an advanced understanding of physics completely redundant to a for example, 9th grader beginning to learn about physics. Ta-da?
No.
It's not a correct application of Newton's Third Law. That is the problem.
Now I have provided you with that little nudge in the right direction, do you think perhaps you could google yourself an explanation as to why?
Or would you like me to spoon-feed you that, too?
Let me provide you with another clue. You can get off the relativity bus, because, as I said several posts ago, Einstein's remarkable improvements on Newton's work have absolutely nothing to do with the topic at hand.
Frankly, I'm dubious about your ability to actually participate in this conversation.