Unable to auto update pass using webservice url

I have added an auto updatable pass to wallet. As soon as it is added I am able to receive the registration request. When there is change available for the pass I am able to trigger push notification to registered device via APNS. I am also able to receive the consecutive call about serial numbers. In the final call made from device to /v1/passes endpoint , server is sending the pass with these headers - Content-Type, Content-Disposition, Last-Modified however the pass is not getting updated. There are no logs received on /v1/log endpoint. From a MacBook when I hit the same endpoint, I am able to download and open the pass. Anything else that is needed on the headers so it can work on device?

Is it necessary to have change description in the updated pass so that pass can update on device?

Adding additional details , I can also see the device tries to pull the pass for somewhere around 20 attempts and then eventually that pass becomes non updatable. Even if you trigger notification to update the pass after the above attempts , the call to retrieve serial number occurs but after that it doesn't make call to /v1/passes endpoint to update the pass.

Unable to auto update pass using webservice url
 
 
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