I am getting the following error when I try to do pod update. once it failed, I am not even able to do pod install anymore.
Installing FBSDKCoreKit (4.36
According to the change log, version 4.36.0 was released yesterday (30th August). It looks like they've forgotten to create a release tag for it yet in their Github repository hosting the Facebook iOS SDK.
In the meantime, you can set your pod to:
pod 'FBSDKCoreKit', '4.35'
pod 'FBSDKLoginKit', '4.35'
pod 'FBSDKShareKit', '4.35'
then pod update.