I totally agree with Ranjeet & Ashish.

But there are some other reasons also which shows a major impact in reporting click link stats between Facebook Ad Campaign & Bitly. 
 

1. Bitly is unable to measure cross device conversions both on Web & Mobile due to it's cookie based measurement but Facebook does it very accurately because people are actually on their platform.
2. If a person does not click the ad post of your product on Facebook but browses the site later and finally decides to purchase, Facebook attributes this conversion but third party apps like bitly identifies only linear conversions where the user clicks the ad & get immediately converted.

That's why there is so much difference between both of them.

Hi Shweta,

If you are using third party tracking tools(Bitly) to record clicks/page views of your destination URL on Facebook ad campaign, your record does not match from the facebook analytics stats, there have several reasons. 

1. I researched on both of them and analyse. According to my research, page visits or page Views by Source FACEBOOK Ad and bitly's clicks tracking methodology is different from facebook stats.

2. To track page clicks, Facebook use user's browser, location, cookies, Javascript etc. In case the cookies are disabled then Facebook may not record and read your page views by source.

3. Usually, 40% of people browse Facebook using HTTPS(Secured Server) instead of HTTP(Unsecured Server) and when someone clicks on an ad on Facebook and converts on a site, the referrer cannot be recorded since they left an HTTPS environment and entered an HTTP environment. This is the drawback of bitly(third party tools) tracking provider.

4. Also if you click a facebook Ads multiple time then facebook will count it as a separate click but Bitly will count the same source as one page clicks (if your javascript and Cookies Disabled).

If you want to know more in details check here- Differences Between third party Ad Reporting and Facebook Ad
 

Hello Shweta,
 

Facebook is a vast social media platform to connect with the large audience. Creating a Facebook Ads Campaign to target the right audience & optimizing ads helps to spend PPC budget.

Few reasons why there is an extreme variance between Facebook Ads Campaign and Bitly click links status such as :

• The Tracking methods also add variance in Ad Campaign. Bitly automatically receives and records information from web browser while using the services, including IP address and cookie information. Whereas Fb Ad campaign uses two methods to track traffic as :
   

Conversion Tracking Pixel :

Facebook use conversion tracking pixel to track conversions on website in which ads is running on Facebook.
 

Custom Audience Pixel :

Custom Audience pixel helps to track visitors to specific pages of the website and turn all visitors into an audience to serve highly relevant Ads.

 

• When the Ad Campaign & Bitly link is used for different time zone, It also adds variance in traffic results.
• Use of Url parameter add difference in the results. URL parameters on ad campaigns helps to identify from where the ad traffic is coming. It also show which link people clicked to get the ad campaign's target destination such as Facebook Page or website.

Hence the data of Facebook Ad Campaign and Bitly will never match. So to get better results for Facebook Ads campaign you can prefer 5 Facebook Ad Tracking Techniques Used in Every Profitable Campaign.