Can't send/receive MMS on Wi-Fi

I have had the same issue on my LG V20 for a year or so now. I finally found a solution that worked for me by accident. If I use T-Mobile Digits and the native SMS app on my LG (only the native one will work) everything seems to working as it was meant to. I only found out about digits a few days ago (not sure why T-Mobile is not advertising it). Digits allows you to use multiple phone numbers on one phone (through cellular data connection or WIFI) and also allows you to use your phone number on other devices as long as it has an internet connection. Some phones have the Digit app as a native app (the V20 does) but you can also download the app. The native version is not activated by default, you have to go to the Digits web app to activate it. It was a bit of a convoluted process and I'm not 100% how I managed it but when I log into my T-Mobile account and click on "phone" it showed me a Digit link below the image of my phone. After clicking that it asked me if I wanted to activate this on my phone. Once activated you have to go to your phones settings, accounts and add the digits account (not sure if this is fully necessary but this will allow you to use multiple phone numbers). Once activated when I opened the LG messenger app on my phone it showed me a magenta sim card symbol next to all my conversations. This now means all the conversation (or at least the new ones) will also show up on which ever other device you register to it. You can even log into it on a web browser at DIGITS de T-Mobile . I'm not 100% sure how this makes it work but I think its because Digits is fully web based it sends all the info as pure data not some hybrid MMS/SMS thing. Hope this works for other people too.