RuntimeError: Model class paypal.standard.ipn.models.PayPalIPN doesn't declare an explicit app_label

解决方案:

pip install django-paypal

然后settings.py中加入

import paypal

INSTALLED_APPS = [
    'django.contrib.admin',
    'django.contrib.auth',
    'django.contrib.contenttypes',
    'django.contrib.sessions',
    'django.contrib.messages',
    'django.contrib.staticfiles',
    'paypal.standard.ipn'
]