Hello,
I have only done paper application for visitors visa but the application form is filled out online, there is a section on the form that asks for the amount of money to plan to travel with and they ask for your occupation. In my country, they usually request a bank statement. I'm thinking the amount of money you planned to travel with for your time here was maybe too little or too much. As for your reason of visit, that's up to you but your letter of invitation (if you have one), return date, etc., are important.
You can always call IRCC and ask the agent if there's additional info on the reason it was refused. I know for a fact that they sometimes have a more detailed reason.