Well, Facebook messanger and iMessage both use internet connectivity to reach your watch and not Text messaging. Could you clarify exactly what type of messages you can't receive from Android based phones?
Basic response:
To receive true Text Messages, SMS/MMS Txt, your iPhone must be on and connected to your carrier's cellular network via cellular connectivity or Wi-Fi Calling connectivity. This is to allow your iPhone to forward your actual "Text" messages to your watch.
Dave