The offline conversions application-programming interface Facebook began testing in June is now available to all managed business accounts via Business Manager.
Business Manager users now have access to a new Offline Events section, and the description for that section follows:
Start uploading data related to offline events, which are business activities that happen outside of Facebook, your website, or your app. You can measure the impact of your Facebook advertising on your business across your sales channel and market based on customer actions.
When Facebook introduced the offline conversions API in June, it said in a Facebook for Business post:
Advertisers now have a way to connect transactions that take place in store or over the phone to their ads. The offline conversions API allows businesses to match transaction data from their customer database or point-of-sale system to ads reporting, helping them better understand the effectiveness of their ads in real-time. Advertisers can use the offline conversions API to:

See real-time results as transactions occur in-store and over the phone.
Gain demographic insights about people who purchase.
Optimize future campaigns.

Facebook said in an email to SocialTimes:
Since then, we?ve introduced permissions and management surfaces in Business Manager, as well as opened the user interface for manual data upload.
Business Manager users: Have you experimented with the offline conversions API yet"

Thank you to Abs Elmaz ...