Unreliable app: "validation error" – Tiny House Magazine Review

I've subscribed to this magazine in the past, and while the content is great, the app is unreliable. Now, I can't even subscribe to the magazine, since it just keeps giving me a "validation error." I've tried a few different Apple IDs and had the same issue. Sent a note to the developers but never heard back.
Review by mreidsma on Tiny House Magazine.