If you receive messages on one device but not the other
If you have an iPhone and another iOS device, like an iPad, your iMessage settings might be set to receive and start messages from your Apple ID instead of your phone number. To check if your phone number is set to send and receive messages, go to Settings > Messages, and tap Send & Receive.
If you don't see your phone number, you can link your iPhone number to your Apple ID so you can send and receive iMessages from your phone number. You can also set up Text Message Forwarding so you can send and receive MMS and SMS messages on all of your Apple devices.
If you have issues with a group message
If you’re in a group message and stop receiving messages, check if you left the conversation. Open Messages and tap the group message. If you see a message that says you left the conversation, then either you left the conversation or you were removed from the group message. You can rejoin a group message only if someone in the group adds you.
To start a new group message:
Open Messages and tap the Compose button to start a new message.
Enter the phone numbers or email addresses of your contacts.
Type your message, then tap the Send button .
If you have other issues with a group message, you might need to delete the conversation and start a new one. To delete a group message:
Open Messages and find the conversation that you want to delete.
Swipe left over the conversation.
Tap Delete.
When you delete a message, you can't recover it. If you want to save parts of a message, take a screenshot. To save an attachment in a message, touch and hold the attachment, tap More, then tap Save.
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