This issue is usually caused by a delay in the processing of your payment. You may try to resolve this by going to Settings > Upgrade. The app should automatically verify your premium membership when you do this.
Should the issue persist, please check in Settings > Connection if you're logged in to the account you used when you upgraded. Please note that your premium membership is linked to a particular Player FM account, thus it is important to log in to the correct account so you can enjoy the app's premium features and avoid encountering issues on premium plan verification.