I would like to purchase a second sim card (for a friend who will join Fizz shortly and doesn't have

You can buy with your credit card, and later on your friend need to have a prepaid credit card, or if you want you can pay with yours

https://fizz.ca/en/faq/what-payment-methods-can-i-use

You can use a Visa or Mastercard credit card (including prepaid), or a Visa Debit card to pay for your Fizz plans.

Other cards such as debit cards, American Express (Amex), Dinners, and others are not accepted. Foreign credit cards are also not accepted. You also cannot use the funds from your Fizz Wallet to pay for your monthly plan.