I can receive a message from a Google Pixel phone, but my reply is not delivering. I just activated an iPhone 6 and this is my first message to this person.

Adding to Julie's question, I am having difficulty sending messages (with images) to a string that has fellow iPhone users on it but one Pixel phone user. The Pixel number used to be an iPhone but is not any longer. When I am addressing my iMessage and enter the two iPhone user's numbers, they appear blue as one would expect for iMessage. Once I add the Pixel phone #, they all turn green, but instead of sending all as sms or some as iMessage and the other as sms, the send fails. Sometimes, it will reach the iPhone users and nothing shows up at all on the Google phone. Any idea how to properly send to a mixed string or overcome this problem without sending the message twice? Thanks much

The pixel user did not de-register their number from iMessage. They need to do that. This is not a problem on your end, it's a problem on theirs.