The comma is wrong. Good catch!

What is the synonym of the word “catch”, please?

I hope to hear from you soon. Thank you so much.

Best wishes.
I think it's kind of a sporting expression. If I'm not mistaken, the quote you refer to involves spotting or spying someone making an error. That is, you "catch" someone in a mistake. If you hadn't "caught" him, he might have gotten away with it. I can't think of a synonym.

In some sports, eg., baseball, they use "good get" as a synonym for "good catch," but it's a fairly new expression. The difference between this and your example is that in baseball you job is to catch the ball - even the difficult ones. When you catch someone making a mistake, you may or may not be looking for violators. You may just "happen" to see it.

Of course, "Good catch!" could refer to fishing.
I agree. There's not really a synonym.

Good observation - I'm glad you found that error.

That's about the closest I can get.