Declines show as "unknown error" in Stripe 6.8 on WP

If you put in a "decline" test card on WP, e.g. 4000 0000 0000 0002 you'll receive "unknown error". On Drupal you receive "payment declined".

The POST request to the ProcessPublic API is returning a 500 from Drupal, but a 200 from WP in this scenario.