Why can’t I send messages in just one conversation on my MacBook Air?

Re: "Why can’t I send messages in just one conversation on my MacBook Air?"

Wondering if a recipient is using an Android device, in which case, instead of wi-fi, their messages need to go via cellular data (green bubbles). (ie: Android users are unlikely to have the Apple software on their phones:)

Apple to Apple devices send and receive messages via wi-fi) (ie:blue bubbles)

Cellular data use would need to be allowed by a provider / plan, switched on and made available to your Mac. (May be able to send to thread recipients via your phone)

You can check the details: Set up iPhone to get SMS, MMS, and RCS messages on Mac - Apple Support

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If needed:

Messages Support website: Messages for iPhone, iPad, Apple Watch, and Mac - Official Apple Support

Re: there is one thread on which I no longer have a new message field on my mac.

You may want to check whether Apple Support's online article can help:

Send an inline reply to a message on Mac - Apple Support

Eg: says:

1. "Go to the Messages app  on your Mac.
2. Select a conversation.
3. Control-click the message or attachment, then choose Reply.
4. Tip: If you have a trackpad or a Magic Mouse, you can swipe right with two fingers on the message or attachment.
5. Enter your message in the field at the bottom of the window, then press Return on your keyboard to send it.

Note: Everyone in a group conversation can see your inline reply. To reply privately, click the name of your group at the top of the conversation, Control-click the icon of the person you want to message privately, then choose Message.

If Apple Intelligence* is turned on, you can use it to suggest a reply to a message you receive. See Use Apple Intelligence in Messages."

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Else: We are all Apple users, like yourself, volunteering our time to do the best we can to assist. Sorry I don't have enough info. about the situation. Trying to trouble-shoot all the other possible causes / solutions, one by one is not economical for this method of communication.

If needed: Try contacting the experts on Apple's Messages support team:

Messages for iPhone, iPad, Apple Watch, and Mac - Official Apple Support

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