App is trying to use wrong SMS agent, sending fails without warning

[otofue]

I am using Nexus 5X with latest Android verson 8.1.0 with security patch level April 5, 2018. SMS-Ticket failed to recognize my default SMS application (which is Signal, not the default Android Messages). SMS-Ticket attempted to send ticket request via (turned off) Messages app. Of course, the SMS was never sent. SMS Ticket is totally unaware of this fact, and is still waiting for the ticket confirmation, which - of course - will never come. There was no warning to the user.
This makes the app useless. It is trying to blindly send via Messages, even if it is turned off and not used for sending or receiving short messages. Please change the Ticket app behavior. It should always use the globally set SMS agent. Thanks.