I am having an issue updating plan payment method, every time I click on "manage subscriptions, it takes me to the login page. and when I log in again, nothing happens.
To follow up, I wanted to thank @Idrissa for bringing this issue to our attention.
We have now updated the Customer Portal so that you will now see the ‘Manage Payments’ button even if all your subscriptions are not active (expired, unpaid, trialing, etc).
For more info about using the Customer Portal, refer to this post.