Hi MinhDNguyen In ARM secureStrings are a data type requiring an encrypted value. It is the most common and popular way of handling secrets in ARM template parameters. If you have a field in an ARM template that specifies a parameter of type secureString, you must pass it an encrypted value. It cannot be null, it cannot be in plain text.
Instead of inserting the text you can use Azure Key Vault to pass strings, you can also create variable groups that could be assigned per environment so you can have different variables for QA and Prod. I plan to get into those things eventually but not this early in the series.
I cannot explain why you are not getting this error, this was the first error I ran into that had to be fixed. I'm glad you are not receiving errors :).