iCloud vs. iMessage?
Apple ID is different than I message? Having a problem using them and having them signed in simultaneously, not sure why.
iMessage is part of a group of iCloud services. Signing into iCloud gives you access to using iMessage.
Use Messages on your iPhone, iPad, or iPod touch - https://support.apple.com/HT201287
If you can't send or receive messages on your iPhone, iPad, or iPod touch' click on this link -->
https://support.apple.com/HT204065