'ServiceAppointment' entity doesn't contain attribute with Name = 'serviceappointmentid' and NameMapping = 'Platform'.

I'm migrating from CRM 365 to CRM online and receiving the following error when trying to import Service Appointment entities.

I've looked through the list of fields in 365 and online and neither contain the field 'serviceappointmentid'.The description error reads 'The specified field does not exist in Microsoft Dynamics 365.'

Any help would be much appreciated, I've been stuck on this for a few days now. 

thanks!

Matt