Charging After Users Have Been Using Product For Free

Hello,
I'm new to Indie Hackers but I feel like I could learn a lot from this community.

I am currently developing an application using the Spotify API. The trouble I have using this is they require written approval in order for me to commercialize my application.

Eventually, my goal is to charge a monthly subscription fee to my users, however, when the application is released I won't have the written consent yet(It could take up to 3 months after release).

I'm trying to decide on what strategy I should use in order to not push users away from the product. I have thoughts of doing a "Get 3 months free" sign up offer. This would give me time to hear back from the application and get their payment information upfront. Ideally, I would be targeting people who would be open to paying for my product in the future.

The other thought is to just offer for free and when I am accepted to commercialize then I will send an email to all of my users and then require payment information to be provided before they can continue using the product.

I'm not sure which path to take, or if there is something I'm overlooking. Any input would be amazing!