CBSubs - PayPal payment gives error (on the paypal side) with 'Message 3514'

We are implementing a Joomla! site with CBSubs for subscriptions for one of our clients, and taking a subscription paying by Paypal is not working. I'm gonna go and be as complete as possible here, sorry if this includes irrelevant info.

MY SITUATION/SETUP
=============

Joomla version: 2.5.
CBSubs version: 3.0.0.

We are using the subscription mainly for selling access to individual articles (which contain a video lesson).

We created a business paypal account, and set up the paypal gateway in CBSubs with the following configuration:

Paypal account: screenshot [REMOVED]
Paypal API credentials: nothing, just left empty
Paypal specific settings: [REMOVED]

Note that the paypal instructions in CB Subs are a bit out of date, paypal organizes its settings in the backend differently (for example PDT is under 'profile' > 'selling tools' > 'website preferences' which is not how it's explained in the CBSubs backend).

However, I think I did manage to find and configure all of the settings mentioned:
- IPN is enabled: [REMOVED]
- Auto Return and Payment Data Transfer are both set to ON (and the 'identity token' in the settings is filled in in the CBSubs section) [REMOVED]
- Payments in foreign currencies:

AHA,maybe it's because we are working in dollars not EUROs??? The payment receiving preferences of paypal state: 'Note: If you are using IPN, you must update your scripts to handle payments in currencies other than U.S. Dollars. Learn More'.

Did you do this???? Maybe y'all are assuming USD somewhere as the vendors currency?

Still in 'payment receiving preferences' (linked to by 'block payments' - ok so it's fucking PayPal that makes its navigation impossible) the 'Block accidental payments' was set to YES, but since it says: 'You may prevent accidental payments by blocking duplicate invoice IDs' this sounds related to my problem. Allow me to set it to NO... NOPE, still doesn't work.

THE PROBLEM/STEPS
=============

In my Joomla site, I go to a protected article (with the stuff below the 'read more...' protected, as documented in the CB Subs documentation). I then proceed to buy a subscription for access, and it sends me to paypal as expected. Also, in the paypal site, I can log in and click 'pay now', after which I would think it pays and returns me to my Joomla! site, subscription now activated.

Instead it shows this:

"We are sorry, we are experiencing temporary difficulties. Please try again later. If this error occurred while making a payment, avoid duplicate payments by checking your Account Overview before resending a payment.

For some browsers, this problem can be resolved by clearing or deleting cookies.

Message 3514"

Screenshot: grab.by/nRXy .

Note that I DID clear cookies as they suggest, but still get the same error.

Thanks for any suggestions fellows!

I've removed many of your screenshot URLs for your safety. Please take those images down and reset all your API keys. These forums are completely public and you've exposed your secure PayPal token to the entire internet. Based off your other screenshots that I've removed your configuration is completely fine.

Reviewing your last screenshot your error is entirely on PayPals end. This can happen if you were logged into Sandbox then switched to Live or vise verse without purging all PayPal cookies. It can also happen if the order id has already been used in another purchase or you've already made a purchase for that order id as PayPal, all gateways actually, don't allow duplicate payments for same order id. You'll need to contact PayPal for more details. There's nothing we can do as the error is on PayPals end.

Doing a quick search it seams like this can happen if you fail to confirm the email address attached to your account, but I don't know specifically if this is your issue or not as the issue is on PayPals end so you'll need to contact their support to help figure out what's going on.