Yes, you will be automatically charged when your subscription runs out.
From May 4th, 2020, RedKiwi is offering the subscription of RedKiwi Premium, not the purchase of RedKiwi Premium. You can always easily change/cancel your subscription settings in the Google Play Store/Apple App Store settings.
Subscribe to RedKiwi Premium and get a ★Free 3-day Trial★ and try out all of the features of RedKiwi! You won't be charged during the trial, so don't be scared to try! Try RedKiwi Premium and choose whether or not you would like to purchase a subscription. 😇
(For your information, there are two types of payment in in-app purchases. One is the subscription(or recurring payment) payment, which means you will be billed automatically on a regular basis(usually every month or year). The other is the purchase, which is just a one-time payment.