Greetings sarahfelldown,
Thanks for visiting the Apple Support Communities! It seems group SMS/MMS messages are failing to send on your iPhone.
Test after deleting the group conversation (make sure to save attachments). If the issue persists, check for an iOS update, and check for a carrier settings update. Reach out to your carrier to check provisioning, as group SMS/MMS route through your wireless carrier if the issue continues:
If you can't send or receive messages on your iPhone, iPad, or iPod touch - Apple Support
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."
Kind regards.
