Error posting with requests

[julio2000]

So I've created a code that posts something on a website. It works perfectly fine when I run it like this (+ other code but that isnt important):

# Above is other (correct) code, wich isnt important
        payload = {
            "firstName": self.first_name,
            "lastName": self.last_name,
            "email": "[email protected]",
            "dateOfBirth": self.dob,
            "termsAccepted": 'true',
            "variantId": int(self.size),
            "articleId": int(self.url),
        }
        response = requests.post(url2, payload, proxies=proxies)
        print(response.status_code)

It prints out '200', so this code works.
But when I run it with the (SAME) email being a variable.
So like this:

# Above is other (correct) code, wich isnt important
        payload = {
            "firstName": self.first_name,
            "lastName": self.last_name,
            "email": self.email,
            "dateOfBirth": self.dob,
            "termsAccepted": 'true',
            "variantId": int(self.size),
            "articleId": int(self.url),
        }
        response = requests.post(url2, payload, proxies=proxies)
        print(response.status_code)

it prints out (500), with the reason: internal server error.

Does someone know why?