You’ll need to set up a proxy to host a bot from. Then you’ll need to create a medium to transfer data.
This devforum post accomplishes what you’re looking for. The bot is hosted on Glitch, the data is sent from discord to Google Sheets and then to ROBLOX. You can theoretically use this data model to send anything to ROBLOX using sheets.
That post has the full setup guide for every part of the bot. Good luck!
EDIT: I totally missed that you already referenced the post in your original. My bad! In terms of sending messages from Discord to ROBLOX, you can still accomplish this task with the google sheets. What I would do is create a key for each player who is sending messages to ROBLOX through discord, and then check (every 30s) the google sheets from ROBLOX. Check every single entry in the row of each Key, given it isn’t empty, and send it, then clear the key’s row.
This does require moderate editing of the original forum post’s code as well as the GS script if you want it to work nicely, but that’s comparitively the easy part of the process.