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You should have two testing accounts by default. Both are eligible to make testing payments at the Oscar store.



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Django Oscar Paypal

Download the repository:
https://github.com/django-oscar/django-oscar-paypal

There is a folder paypal inside. 
Copy folder paypal to our project folder root (mysite).

pip install paypalhttp
pip install paypal-checkout-serversdk
pip install django-localflavor

INSTALLED_APPS = [
    ...
    'paypal',
]

PAYPAL_SANDBOX_MODE = True
PAYPAL_CALLBACK_HTTPS = False
PAYPAL_API_VERSION = '119'

PAYPAL_API_USERNAME = 'sdk-three_api1.sdk.com'
PAYPAL_API_PASSWORD = 'QFZCWN5HZM8VBG7Q'
PAYPAL_API_SIGNATURE = 'A-IzJhZZjhg29XQ2qnhapuwxIDzyAZQ92FRP5dqBzVesOkzbdUONzmOU'

urlpatterns = [
    ...
    path('checkout/paypal/', include('paypal.express.urls')),
]

...
<li><a href="https://github.com/django-oscar/django-oscar-paypal">
    {% if anon_checkout_allowed or request.user.is_authenticated %}
        <a href="{% url 'paypal-redirect' %}">
            <img src="https://www.paypal.com/en_US/i/btn/btn_xpressCheckout.gif" align="left" style="margin-right:7px;">
        </a>
    {% endif %}
</li>
...

Removing «Ship to» in paypal checkout window: (Optional)

class RedirectView(CheckoutSessionMixin, RedirectView):
    ...

    as_payment_method = True

    ...

    def _get_paypal_params(self):
        """
        Return any additional PayPal parameters
        """
        params = {}
        params['NOSHIPPING'] = 1 

        return params

python manage.py makemigrations
python manage.py migrate

Next step is to change Paypal from sandbox to production and start accepting real payments.