After setting up my dual SIM infinix Hot 2 smartphone powered by Android One and Android 5.1 lollipop, I couldn’t send sms using the “Messenger” app not until I set a preferred SIM for SMS messages via the “Settings” app.  
“No Preferred SIM Selected for Sending SMS Messages” keeps popping up everytime and SMS won’t send even after long pressing the send button to select the SIM to use.
So, if you’re experiencing same problem, all you need to do is to set a preferred SIM for SMS messages.
To do this,
==> Launch the “Settings” app
==> Tap “SIM Card”
==> Tap “SMS Messages” option under “Preferred SIM for :”
==> Select the SIM card you want to set as the preferred SIM.
Thereafter, go to the ‘Messenger” app to send your messages.
If you want to use the second SIM, long press the “Send” icon and select it before sending the message.
Happy Texting!