The Unable to Complete Cellular Plan Change error message is related to an installation failure which can be caused by different factors as follows: 
1. Too many eSIMs are installed on the device. eSIM compatible devices allow you to install multiple eSIMs, but depending on the device model, the number of eSIMs you can have active simultaneously may vary. For example, iPhones can store from 5 to 10 eSIMs depending on the device's storage. For more information, please contact your phone manufacturer.
- If you confirm that you have maximized your device's eSIM storage. You can remove your old eSIMs on the device. You may see the instructions on how to remove eSIMs here: How can I remove an eSIM from my device?
2. Cellular/Mobile data is disabled in the device's settings







