Create Customer Portal Session

curl -X POST "https://api.devkit4ai.com/api/v1/payments/stripe/customer-portal?test_mode=true" \
  -H "Authorization: Bearer {end_user_jwt}" \
  -H "Content-Type: application/json" \
  -d '{
    "return_url": "https://myapp.com/account/billing"
  }'

{
  "portal_url": "https://billing.stripe.com/p/session/test_YWNjdF8xQUJDMTIzZG"
}

// Manage billing button component
function ManageBillingButton() {
  const [loading, setLoading] = useState(false);

  const handleManageBilling = async () => {
    setLoading(true);
    try {
      const response = await fetch('/api/customer-portal', {
        method: 'POST',
        headers: { 'Content-Type': 'application/json' },
        body: JSON.stringify({
          return_url: window.location.href
        })
      });
      
      const { portal_url } = await response.json();
      window.location.href = portal_url;
    } catch (error) {
      console.error('Failed to open portal:', error);
    } finally {
      setLoading(false);
    }
  };

  return (
    <button onClick={handleManageBilling} disabled={loading}>
      {loading ? 'Loading...' : 'Manage Billing'}
    </button>
  );
}