I have posted support ticket about issue with api - two days ago and no answer.
Ticket ID: 30480
Several api endpoints are broken and always return 500 internal server error. This behaviour continues for at least 72 hours! It can not be client issue - your api UI at https://api.hitbtc.com/api/2/explore/ also gets this kind of response.
At least, api is broken at endpoint /api/2/account/transfer

72 hours downtime is unbelievable for  "the most advanced cryptocurrency exchange"

Will this issue ever be fixed?