Try deleting the conversation in iMessage first. Then send your message, it’ll allow you to choose which line to send from.
You can’t use iMessage on both accounts, only one. The other is SMS only. No idea why this is ♂️
When you set up iMessage, it's only available for one number, not two. I've read some theories that Apple will introduce dual iMessage ability in the future. Whenever that is. This poses a problem for people who are involved in iMessage group chats because the non-iMessage party won't receive those texts.
So from either line I should be able to send green sms messages right?
Only if you turn off iMessage.
What if they are on an android...wouldn’t it just be sms automatically?