Help With Webhook and Texts?

So I have a webhook script and everything is working perfectly. The only problem is, when I try making a value equal a text, it prints the text's value before it is changed. I tried using a FocusLost function and a GetPropertyChangedSignal and it I get the HTTP 400 Bad Request error. How could I make it detect when the text is changed?

local data = HttpService:JSONEncode({
        ['username'] = 'Training Initiated',
            ['embeds'] = {{
                title = "**" .. player.Name .. " has initiated a training!**",
                description = "[A training is taking place on Novira Resurge Recruitment Center](https://www.roblox.com/games/3614503911/Noviran-Resurge-Recruitment-Centre).",
                color = 16711680,
                thumbnail = {
                    url = "https://cdn.discordapp.com/attachments/548348433803640834/618639311578857492/ForTragic.png"
                },
                fields = {
                    {
                        name = 'Host:',
                        value = player.Name,
                        inline = true
                    },
                    {
                        name = 'Co-Host',
                        value = player.PlayerGui.CreateTrainingGui.CoHost:GetPropertyChangedSignal("Text"),
                        inline = true
                    },
                    {
                        name = 'Type of Event:',
                        value = "N/A",
                        inline = true
                    },      
                    {
                        name = 'Rank(s):',
                        value = "N/A",
                        inline = true
                    }
                },
                footer = {
                    text = "{volgrok100 Training System}"
                },
            }},
        ["content"] = "@everyone " .. "**" .. player.Name .. "**" .. " is hosting a training!"
    })

    HttpService:PostAsync(URL, data)