Can we use sql express for this? is it leagle?

Can we use sql express for this? is it leagle?

I also have same problem. Can any one give us a answer?

Yes, you can use SQL Express in Production as long the database is not larger then 10 GB (SQL Express 2016).
SQL Express 2016 are limited to use 4 cores and 1410 MB Memory per instance.

https://www.microsoft.com/en-us/sql-server/sql-server-2016-editions