Can someone give me the script to log in fiverr.com and fetch my message from inbox using cURL PHP

No I don't have any. I just want to automatically check my Inbox and copy it down from fiverr.com using cURL PHP

you need to know the fiverr form processor location to be able to do this outside the API protocol. Look for something like this on their website

<form method="post" action="thisLocation/file.php">

You will also need to know the exact form attibutes e.g.

<input type="text" name="thisAttr" />
<input type="password" name="thisOneAlso"/>

Look for any hidden input as in

<input type="hidden" name="thisOne" value="youNeedThisAlso"/>
<input type="hidden" name="loginTransaction" value="youNeedThis"/>

Look for transaction ID and session key most of the time it is delivered by javascript OR in hidden form input.

Without those info. we cannot use cURL. cURL function as if you are physically logging in, and it does the job for you by providing the input necessary for the form to be processed.