Why did Elisha allow Naaman to bow before Rimmon?

[TonyChanYT]

2 Kings 5

18 But may the Lord forgive your servant for this one thing: When my master enters the temple of Rimmon to bow down and he is leaning on my arm and I have to bow there also—when I bow down in the temple of Rimmon, may the Lord forgive your servant for this.”
19“Go in peace,” Elisha said.

Elisha allowed Naaman to bow before the idol Rimmon. On the other hand, Zephaniah 1

5those who bow in worship on the rooftops to the stars in the sky; those who bow and pledge loyalty to the Lord but also pledge loyalty to Milcom

How to reconcile 2 Kings 5:19 and Zephaniah 1:5?

Elisha was being gracious and merciful to Naaman, a Gentile. He could have thrown the book at him and quoted the 2nd commandment, Exodus 20:

4“You shall not make for yourself an image in the form of anything in heaven above or on the earth beneath or in the waters below. 5You shall not bow down to them or worship them; for I, the Lord your God, am a jealous God, punishing the children for the sin of the parents to the third and fourth generation of those who hate me, 6but showing love to a thousand generations of those who love me and keep my commandments.

Was God being unjust by being nice to Naaman and not so nice to the Israelites?

Romans 9:

14 What then shall we say? Is God unjust? Not at all! 15 For he says to Moses,
“I will have mercy on whom I have mercy,
and I will have compassion on whom I have compassion.”

The more we know of God, the more God expects of us.

How to reconcile Naaman's bowing in 2 Kings 5:19 and bowing in Zephaniah 1:5?

In the case of Zephaniah, the Israelites had direct revelations from God through Moses and the prophets. God expected more from them. Naaman was a Gentile. God extended a special grace to him individually, a special case, by allowing him to bow before idols while his heart was with the true God.