"Your server is sending an empty fbc parameter..."

Hey peops,

I’m getting this message in the Match Quality screen on Facebook:

“Your server is sending an empty fbc parameter through Conversions API, but we observe a valid fbc parameter being received through Meta Pixel.”

When I check my server GTM in preview mode the fbc parameter is fully present and correct, and is being sent in the outgoing HTTP request to FB from sGTM.

What might be going on? Thanks