Unable to Complete Data Plan Change. Your data plan could not be set up. Try again later.
This error usually indicates that the connection to download the eSIM plan was not made. Your devices needs a stable internet connection to request and download the eSIM profile for the first time.
This error will also show if an eSIM has been removed and a 2nd attempt to add the eSIM profile using the same QR code is made.
Here are some other trouble shooting tips from Apple on how to fix any issues you might encounter when using Dual SIM with iPhone XS, iPhone XS Max, iPhone XR, or later models that feature a nano-SIM card and an eSIM.