Using your analytics platform to hold information about offline activity and conversions, that started with an online journey, is the best solution to problem. This will give you a solution that works for all your online efforts and not just a specific ad platform.
For this to work, you need to make it possible for users to share an ID between their online sessions and your CRM database. This is then used to record what happens with the customer once you have their details.
There are two possible ways to do this, by using either the UserID method, which is the most effective, or the Client ID method.
Here’s how you can implement these changes: