HTTP Error 400 (Bad Request)

I am making a webhook for Google Chat but it keeps giving me this error:
“HTTP Error 400 (Bad Request”.
Does anyone know how to fix it?

(Here is the section of the script giving the error:)

local webhook = "" 
local HTTP = game:GetService("HttpService")
local input =  "test message"

local payload = HTTP:JSONEncode({
	content = input;
    username = "bingus"

HTTP:PostAsync(webhook, payload)

Apparently it does not exist?

the webhook does exist i have proof