Signature for IOS

Good morning. I have a Litchi subscription on my Google account. I’m going to change my device to an iPhone and I want to know if I can use the same subscription or if I have to buy another one for the same user?

You will have to purchase Litchi again. This is from the Litchi Help site - FAQ

10. I purchased the app on one device, can I install it on other devices?

You can install the app on as many devices as you want as long as they use the same platform and the same “main” account (Google, Apple or Amazon) that was used for the original purchase. If you wish to use Litchi on two or more platforms you will need to purchase it on each one.