I just tried to set up Hydroxide to use as an SMTP proxy; but I'm hitting some kind of error.

hydroxide auth <username> works and initializes things as I'd expect; and my SMTP client is connecting properly.

I see the following error when the SMTP client tries to send an email:

smtp: Failed: 454 4.7.0 [2000] Invalid input
Sending failed: Temporary error in sending the message

When I look at the console output from hydroxide smtp, I see the following corresponding error:

2019/09/27 03:03:21 request failed: POST https://mail.protonmail.com/api/auth/refresh: [2000] Invalid input

My best guess is that something has changed about the https://mail.protonmail.com/api/auth/refresh API which is breaking things?