Hello Pipamus-Prime,
Thank you for reaching out to Apple Support Communities, and we'll be happy to help in any way we can. We understand you're having issues with MMS messaging. If restarting doesn't resolve the issue, try the steps listed here: If you can't send or receive messages on your iPhone or iPad - Apple Support
"If you still need help
- Try to restart your iPhone or iPad.
- Check your network connection. To send a message as iMessage or MMS, you need a cellular data or Wi-Fi connection. To send an SMS message, you need cellular network connection. If you turn on Wi-Fi Calling, you can send SMS messages over Wi-Fi.
- Check with your carrier to see if the type of message you’re trying to send, like MMS or SMS, is supported.
- If you’re trying to send group MMS messages on an iPhone, go to Settings > Messages and turn on MMS Messaging. If you don't see an option to turn on MMS Messaging or Group Messaging on your iPhone, then your carrier might not support this feature.
- Make sure that your device has enough space to receive images and videos.
- Make sure that you entered the correct phone number or email address for the contact."
Also, does your iPhone need updating to iOS 16.5.1? Do you have a recent backup for the data in your iPhone in iCloud or your computer? If not, we recommend that you create one as described here: How to back up your iPhone, iPad, and iPod touch - Apple Support
Then update your iOS as outlined here: Update your iPhone or iPad - Apple Support
As MMS messaging is routed through your wireless carrier, the next step we would recommend is contacting them to check the provisioning on your account and possible issues with their network.
We hope this helps.
Cheers!