@Luvl3y
The reason this is occurring is because most servers use IW4M admin in order to detect VPN users trying to evade bans. Your IP is flagged as a VPN IP address.
Try restarting your router to get a new IP if its dynamically assigned.
Otheriwse, if your IP assigns your IP you'll need to contact them in order to get a different IP.
https://forum.plutonium.pw/topic/14/server-advertising-promotion-and-introduction-thread
Alternatively, check this thread for the server's socials and try and contact the owner in order to get your IP whitelisted.