When forwarding the message, are you sending a screenshot or are you copying the text of the message and then sending just the text to 7726?
Sending a picture will not work, you need to send just the text. On most phones, you can do this by just holding down on the body of the text and then pressing forward.
I hope that helps!
I seem to have fixed my issue of not being able to send MMS messages, while SMS and everything else worked OK on my Andriod device with fido network.
The phone was would not send MMS when I was on a wifi network. Sometimes it owuld take hours before any MMS messages came in or went out and other times it would show a failure on the next day.
It turned out to be related to my 'Wi-Fi Calling' setting. If it is on, then apparently MMS will try to go through WiFi too and it fails. I turned 'Wi-Fi Calling' off and now MMS messages go out instantaneously.
I think your issue is slightly different than the one mentioned by the OP in this thread. The system for reporting SPAM messages is not able to accept MMS, only SMS to 7726.
Your issue of not being able to send MMS seemed to be generalised to Wifi and not only to the SPAM reporting system. I think Wifi-calling is supposed to be able to send and receive MMS. I was able to do so using Android 10 and earlier (at least for my phone). It only became an issue upon updating to Android 11. Android appears to have added a new setting (see here). As I mentioned in that post, I can't seem to locate that setting anymore. My phone offered the setting to me when I received a MMS while connect with Wifi-calling. With the Send & Receive when mobile data is off setting is enabled, I can now send and receive MMS using Wifi-calling.
If you can't readily locate that setting, you might consider searching online for that setting and your particular device.
Hope this helps 😀