I have a question for the above error. I understand this happens when information entered in the .env is wrong. However, I have checked. Deleted, started again. There seem to be a problem that the details entered is not being passover. So in my log it says -

    PWD: None
    RETURNURL: http://localhost:8000/en-gb/checkout/paypal/preview/8/
    SIGNATURE: None
    USER: None
    VERSION: 119
    DEBUG 2017-04-27 20:33:12,404 gateway 6804 4513112064 Response with params:
   ACK: Failure
   BUILD: 32996991
   CORRELATIONID: 1762ae0537774
   L_ERRORCODE0: 10002
   L_LONGMESSAGE0: Security header is not valid
   L_SEVERITYCODE0: Error
   L_SHORTMESSAGE0: Security error

Here are me .env

   #PAYPAL SETTINGS
   export PAYPAL_API_USERNAME=mypaypalusername.com
   export PAYPAL_API_PASSWORD=my_password
   export PAYPAL_API_SIGNATURE=my_signature.

in my settings

  import paypalrestsdk
  #PAYPAL SETTINGS

  PAYPAL_API_USERNAME=os.environ.get("PAYPAL_API_USERNAME")
  PAYPAL_API_PASSWORD=os.environ.get("PAYPAL_API_PASSWORD")
  PAYPAL_API_SIGNATURE=os.environ.get("PAYPAL_API_SIGNATURE")

Any reasons why the above settings is not picking data from my .env and passing it over? I am still in the sandbox testing.

Thanking you in advance.