Stripe Checkout - Subscription Issue with Recognized Stripe User - php

Question

I have Stripe working great. Upon a customer's donation, a new Subscription is created, and it works great - except if Stripe recognizes the email and says, "Enter the verification code."
If the customer does that, for some reason, a new subscription is not created and the customer is not charged.
Here is my charge-monthly.php
<?php
require_once('init.php');
// Set your secret key: remember to change this to your live secret key in production
// See your keys here https://dashboard.stripe.com/account/apikeys
\Stripe\Stripe::setApiKey("sk_test_**************");
// Get the credit card details submitted by the form
$token = $_POST['stripeToken'];
$email = $_POST['stripeEmail'];
$amount = $_POST['amount'];
$finalamount = $amount * 100;
$dollars = ".00";
$plan = "/month";
$dash = " - ";
$monthlyplan = $amount .$dollars .$plan .$dash .$email;
//Create monthly plan
$plan = \Stripe\Plan::create(array(
"name" => $monthlyplan,
"id" => $monthlyplan,
"interval" => "month",
"currency" => "usd",
"amount" => $finalamount,
));
// Create a Customer
$customer = \Stripe\Customer::create(array(
"source" => $token,
"description" => "MONTHLY DONATION",
"plan" => $monthlyplan,
"email" => $email, )
);
?>
Any ideas why when Stripe recognizes the user and he is "logged in" it does not allow me to create a subscription?
In the Stripe log, I receive this 400 error:
{
"error": {
"type": "invalid_request_error",
"message": "Plan already exists."
}
}
But there definitely isn't a plan created... ah!

Answer 1

The reason your request is failing is because if a user comes back with the same email address and wants to sign up for the same plan, you already have an existing plan with that name,
$monthlyplan = $amount .$dollars .$plan .$dash .$email;
so your call to \Stripe\Plan::create will return an error and cause the rest of your calls to fail here.
You could add something like a unique id or time to your plan id.
http://php.net/manual/en/function.time.php
http://php.net/manual/en/function.uniqid.php
Some other ways that folks typically handle this are:
Create a single plan for $1, and then adjust the quantity when creating your subscription. So a monthly plan for $1 with quantity of 100, would charge $100 month.
Store the amount that a customer will pay within your application. Subscribe your customers to a $0/month plan. Use webhooks to listen for invoice.created events. Have your webhook handler add an Invoice Item every month for the balance.