In 2017 Google deployed a new Google Ads interface, but not everyone will be migrated to it until 2018.
With that in mind, we have 2 sets of instructions below, for the old and new interfaces.
If you have the NEW AdWords interface, follow these instructions:
NEW Google Ads Interface: How to find your account CID
NEW Google Ads Interface: How to find and accept our link request
If you have the older AdWords interface, follow these instructions:
OLD AdWords Interface: How to find your account CID
OLD AdWords Interface: How to find and accept our link request