Hi @KristiLogos ,
now I understand the problem. 🙂
You have a json and then you want to save this to delta table as struct, right?
The allowed characters for delta table column names are:

Letters: A-Z, a-z
Digits: 0-9
Underscores: _

The key here is that your structs must also adhere to this naming convention
Before saving structs to table you need to sanitize the column names like that:

App Brnd -> App_Brnd
Active.Elapsed Minutes -> Active_Elapsed_Minutes

Hope it helps