I have been trying to upgrade a subscription, but the Stripe system refuses to accept my card. Can you help me with a solution?  

If your card refuses to accept payment from Stripe, you can subscribe from your phone.

1. If you use an Android phone, upgrade through the google play store.

2. If you are an Apple user, upgrade through the iOS store.

Afterwards, you can use the ChordU web version with the same email address.