Error response

### Response codes
HTTP statusDescription
200Successful request.
400Invalid request, see message in the response.
404The OTP was not found.
500Unknown error occurred.
### Error codes
Error codeDescription
1000Unknown error
1001Invalid request
2000Validation error
2001Invalid `channel` field
2002Invalid `from` field
2003Invalid `to` field
2004Invalid `message` field
2005Invalid `digits` field
2006Invalid `expiry` field
2007Invalid `locale` field
2008Invalid `pushAppKey` field
2009Invalid `anonymous` field
3001OTP was not found
3002OTP has expired
3003OTP is already verified
3004Too many attempts
3005Channel not configured
3006Subscription is required
4001Failed to sent message

Error code	Description
1000	Unknown error
1001	Invalid request
2000	Validation error
2001	Invalid ``channel`` field
2002	Invalid ``from`` field
2003	Invalid ``to`` field
2004	Invalid ``message`` field
2005	Invalid ``digits`` field
2006	Invalid ``expiry`` field
2007	Invalid ``locale`` field
2008	Invalid ``pushAppKey`` field
2009	Invalid ``anonymous`` field
3001	OTP was not found
3002	OTP has expired
3003	OTP is already verified
3004	Too many attempts
3005	Channel not configured
3006	Subscription is required
4001	Failed to sent message