payments: invalid api key (or other errors) → no error in UI

[haraldschilly]

I've the wrong api key in my test config.
In frontend settings/purchases, when I try to "add money", it fails silently.

In the JavaScript console, I do see this, though:

app-812... Error parsing response JSON from /api/v2/purchases/create-credit.
Response text: Object text:
"{\"error\":\"Invalid API Key provided: [...slightly mangled key...]\"}"[[Prototype]]: Object

1. I think that endpoint should just return a more generic error and not whatever the actual error was (log the real error server side only).
2. the error should obviously surface and report it to the user, e.g. "sorry, making purchases is currently unavailable, contact support"