You must change your billing information on the platform where you signed up for your subscription - either on the App Store or on our Desktop Site.
Check where you signed up on the iOS apps:
Tap on Profile in the bottom menu bar
Tap on your Collection in the middle of the screen
Tap "Subscription". A pop-up will appear explaining what platform your subscription is affiliated with.
If you purchased on the App Store:
If you pay for InVintory through the App Store, all your payment information lives with Apple.
Just update the credit card associated with your Apple ID.
If you purchased on our Desktop Site:
Click on your profile icon in the top right corner
Select "Account"
Under your profile icon, move from the "General" tab to "Billing"
Click "Update billing information"
You will be redirected to a payment portal where you can add / modify payment methods