Hi Telepaul34,
Thank you for using Apple Support Communities. Based on what you stated, it seems you are able to send messages but not to one specific group. I would recommend you read this article, it may be able to help troubleshoot the issue.
If you can't send or receive messages on your iPhone, iPad, or iPod touch - Apple Support
Sometimes your messages won't send to a particular contact, or you might have issues with group messages. For example, you might reply to a group conversation and receive your own message. Or you might get a new phone number and see your old one listed as a recipient in an existing group conversation.
Delete the conversation* that has the issue and start a new conversation:
- Open Messages and look at your list of conversations.
- Swipe from right to left on the conversation you want to delete. Then tap Delete.
- Open Messages, tap
, and enter the phone number or email address of your contact or contacts.
- Write a new message and tap send.
Cheers