I have built a stripe customer portal using the dashboard and setup product upgrades and downgrades for subscriptions. When I build a customer manually in the dashboard, I can see the upgrades in the portal, but when I use the checkout to create a customer, that customer can't see any upgrades.
Any idea what's going wrong here? Seems like it might be bug on their end.
There are certain limitations involving upgrades for Customer Portal, especially if you are using Automatic Tax. You can see those limitations here. If you don't believe any of those apply, then I'd recommend contacting their Support team at https://support.stripe.com/contact/login with full details.