@Yadu If you can, check the logs on your MR600, they might tell what's going on

Question: What do the router's logs say about your problem? (I have a MR600 v2, but it should be in Advance -> System -> Logs) Also, try to update your MR6400 to the latest firmware

In your MR600v1, Advanced -> Network -> Internet -> change the band option to 'manual'

You're trying to update your MR6400v5, but it's telling you that the file is not correct? Did you try to redownload the file again? it sounds like you got a bad file or the file got corrupted somehow

@masoly If you're talking about turning your MR600 into a VPN client, then it's not possible as NordVPN removed PPTP/IPSec support back in in 2018, and the MR600 uses PPTP as protocol.

Mind if I ask where are you located, just to check what is the latest firmware for your MR600 v2? (I'm just another user of the router) (in response to @IHaveThePower)