User mapping problem during deployment
You have to create a login on the prod server as when you restore the backup to PROD server, you are having an orphaned user.

So steps are :


Create Login using SID option (if you are just having 1 login to map). Else use sp_help_revlogin
You can use SID from sys.database_principals where type_desc = SQL_USER (since you mentioned you are using SQL Login).
Then run ALTER USER as below :

USE [DatabaseName]
go
ALTER USER [UserName]
WITH LOGIN = [UserName]



Note: sp_change_users_login is deprecated.