I wanted to join a clan; a user tried to invite me a but no pop-up appeared. I'm not getting a invitation into my chat box. P.S My chat filters is ON and i already left my previous clan. What could be causing this issue?
I can see from your RuneMetrics profile that you're not in a clan, just to confirm that's definitely not the issue. Assuming this person sent you an invite to join their clan, you should get a message in your chat box stating this person has invited you to join their clan. This message needs to be clicked to accept the clan invitation.
From what you said, it sounds like there was no message indicating a clan invitation was received by you. This would mean the issue lies on the person who attempted to recruit you.
My assumptions, based on the information you've given, are the person who tried to recruit you doesn't know how to invite new players to a clan, or the person who tried to recruit you doesn't have the permission enabled (based on their rank in their clan) to recruit new members. Recruiting permissions are individually set by rank, so this may differ between clans depending on whether they allow all of their members to recruit or not.
The button to recruit new members to a clan is located at the bottom of the clan chat tab:
The setting to enable ranks' abilities to recruit is in the Admin tab of Permission Settings: