You should never be prompted to enter credit card or bank information in a GPT-Play app in order to qualify for a gift card. Since most of these apps use gift cards or store credit to reimburse their users, they can credit you through an email address.
You don't need to worry too much about your banking information, either. In fact, you're already sharing most of this information with your social media and browser providers. However, it is worth noting that there's little a developer can do with this data other than sending more targeted advertisements.
