Client Interview before releasing OL of Globallogic

Hi there GVers,

I was interviewed at GL , passed 3 tech rounds. And today after almost 20 days hr said before releasing the offer letter , clients want to interview.

Now i am feeling nervous.

Is this general procedure for Service based company that clients also take interviews or is it just for me ?

Any other advice is also appreciated.

YOE : 3 years Tech stack : MERN