Where to find Origin Product Code Sims 4?

So I've made my origin account, and am in the process of installing my game (it's a disk copy). It asks me for my origin product code. I've tried inputting the code from the 'Welcome to the Sims 4!' sheet inside the box, but it doesn't work so I'm assuming that's not it. Online it tells me the product code should be sent to me via email; but it hasn't - I just have the 'Welcome to Origin' email and an email about email verification. Please help!