c#

public class unknownCapabilityException : RFC8807Error
{
    public unknownCapabilityException(string detail, int status = 400)
    {
        base.type = "urn:ietf:params:jmap:error:unknownCapability";
        base.title = "Unknown Capability";
        base.detail = detail;
        base.status = status;
    }
}

...

var errorValue = new unknownCapabilityException(errorDetail, 405);

c#

public class unknownCapabilityException : RFC8807Error
{
    public unknownCapabilityException(string detail, int status = 400)
    {
        base.type = "urn:ietf:params:jmap:error:unknownCapability";
        base.title = "Unknown Capability";
        base.detail = detail;
        base.status = status;
    }
}

...

var errorValue = new unknownCapabilityException(errorDetail, 405);