Hey @Ajay Mamgain! I just caught up on your support ticket and wanted to circle back for anyone following along. After digging into our logs for this, we were able to locate a more granular error message that reads:
"message": "(#10) You do not have permission to upload events to this offline event set.The action requires that you must at least be either the event set uploader or business admin.",
Next steps here would be to confirm that the FB account that's being used in the Zap is either the event set uploader or business admin.
From there, it looks like you were asking about how best to import offline conversions from Marketo Webhooks into Facebook, to which my colleague Liam suggested:
It should be possible to use the Facebook Conversions with the new partner integration. I have a helpful guide that provides more information on the integration here: https://developers.facebook.com/docs/marketing-api/conversions-api/guides/zapier-integration/
Hope that helps!