@Bibek_Yadav 

From the photo RE200 connect to router's 2.4 GHz Wi-Fi, sometimes it may take a few secs before the ' Exclamation' mark turn into 'Check 'mark when you refresh the web page.  Ensure you have put RE in a proper location and see if RE has stable Internet 

How to place your wireless Range Extender for optimal reception and performance?
https://community.tp-link.com/en/home/forum/topic/269204

You could follow the guide below and select a better channel on the main router , turn off some advanced wifi settings on router and see if it helps with stability: 

[Troubleshooting] Range Extender Keeps Losing Connection

https://community.tp-link.com/en/home/forum/topic/272398

Can you check the Leds Status on RE200 when error occurs,  Wi-Fi LEDs are ON or go off at that time? May I know the model of router as well, thank you. 

@Bibek_Yadav  Hello, 

May I know the model of your router, does range extender connect to router directly or through other extender or APs?

1. From the photo RE200 connects to 2.4Ghz of router, you could  try a different Wi-Fi channel on router: ( you may need help from router support for this)

Scan for nearly Wi-Fi channels using Wi-Fi analyzer app or software and select a less crowded channel for router.

2.How about the Leds status when the error occurs on the range extender?

If Led is On you could also try the suggestion to turn on DHCP and set up a smaller IP range for RE200 as the guide I sent above.

 Page4 is the Led on RE200: https://static.tp-link.com/2020/202009/20200917/1910012838_RE200%205.0%20&%20RE220%203.0_UG_REV5.0.0.pdf

@Bibek_Yadav Hello, 

Thanks so much for sharing all the detailed info, this issue you are experiencing sounds unusual. To address the issue and try to fix it, we would like to have a specialist look into this further via email. Please check your mailbox later, and let us know if the issue is resolved. Thank you!