Facebook app does not send phone number with purchase events via CAPI

Shopify Partner
112 18 20

When the facebook app sends purchase events to facebook via capi it fails to send the order phone number.

I identified the request sent by trekkie to the backend and the phone prop is always null regardless of the fact that I set order shipping address phone, billing address phone as well as customer account phone.

Wondering if anyone else has this issue and/or any pointers on how to resolve it.