Quick answer
Correction is repaid later, flattery is repaid now, and the verse says which balance ends up larger.
Read both lines
Everything is in the word afterward. The verse concedes the immediate situation entirely: right now the flatterer is doing better, and the person telling the truth is not. It does not pretend otherwise, which is why it is usable by anyone who has actually had to correct someone.
The second half names flattery as a tongue activity, מַחֲלִיק לָשׁוֹן, smoothing with the tongue, which is the same figure 29:5 uses of a man spreading a net. Chapter 27 said the constructive version at 27:6, where the wounds of a friend are faithful. The three verses together assume the same thing: the person on the receiving end eventually works out which one was for them.
Related: Proverbs 27:6 · Proverbs 29:5 · Proverbs 27:5 · Proverbs 26:28
New King James Version®, Copyright © 1982, Thomas Nelson. All rights reserved. Full copyright information. Scripture provided by API.Bible.
Go Deeper
If this verse has been used to put weight on you that it was never carrying, ask about it directly.