Hello Magoochy,
Thanks for using Apple Support Communities.
If I understand your post correctly you are unable to send messages to a specific contact from your iPad. To start troubleshooting this issue I suggest that you go through the steps outlined below.
- Make sure that you're using the right phone number or email address.
- Go to Settings > Messages > Blocked and make sure that they're not on your block list.
If you can't send messages to a certain recipient, delete any conversations you have with them and try sending a new message. When you delete a conversation, you won’t be able to recover it. Make sure that you take a screenshot or forward any messages that you want to keep.
- Restart your device.
- Check for a carrier settings update.
- Check for an iOS software update.
If you can't send or receive messages on your iPhone, iPad, or iPod touch - Apple Support
Take care.