Correct me if I am wrong but the process is simply exporting the request out of Meraki by downloading a file and then importing that into Apples system without any copying and pasting??
If thats the case I would contact support and open a case, its been a long time since I did this but I don't recall it being difficult.
Try this site, it my give you some info and you might be able to find where you are going wrong.
https://documentation.meraki.com/SM/Device_Enrollment/Apple_MDM_Push_Certificate
If you found this post helpful, please give it Kudos. If my answer solves your problem, please click Accept as Solution so others can benefit from it.