We were dealing with this for a while and had to reset the device multiple times, and eventually it would go through. It seemed to like ethernet better than wireless.
As we are piloting another MDM I will say that their DEP sync is just about instantaneous and Meraki's often gets going only very slowly and requires page refreshes to feel better about its task at hand. 😛
I had this error with an iPad running iOS 12 when I assigned DEP settings to it that had items relevant to iOS 13 only. Normally I configure settings to skip most configuration steps like Apple ID, Fingerprint etc. There are two sets in DEP at the moment, one was created when iOS 12 came out and another when iOS 13 came out. There are more things to skip in iOS 13 than in iOS 12. So I thought I could use iOS 13 one for everything and DEP settings would apply to relevant items to devices running older iOS but it just didn't work outright. I had to restore an iPad in question and assign "iOS 12" settings profile in DEP.