[SOLVED] Paypal Error - invoice has already been paid

Joomla version: 3.3.6
Community Builder: 2.0.4
CB Subs: 4.0.0-rc.1

I register a new user and try to pay a subscription with paypal. After the redirection to paypal I Login and pay. Than I get the following error.

"This invoice has already been paid. For more information, please contact the merchant.
Your purchase couldn't be completed
There's a problem with the merchant's PayPal account. Please try again later."

This happens with a complete new registered user and a new created Paypal-Sandbox-buyer-email with there I login into paypal.

Here are my Paypal Website Payment Preferences in my Sandbox-Merchant account:
Auto Return: On
Return URL: www.mywebsite.com
Payment Data Transfer: On
Identity Token: xxx_mytoken_xxx
Block Non-encrypted Website Payment: Off

Paypal runs in Sandbox. So where is my mistake???

Ok I have set (in merchant paypal sandbox account) in Payment Receiving Preferences the option "Block accidental payments:" to "No, allow multiple payments per invoice ID".

But now I have another problem. If I try to pay. I login with my buyer paypal sandbox account and pay. Than I see the following site...



After a few seconds I would not redirected to my site. I am redirected to the paypal sandbox login page.



So why I was not redirected? I cant start with my site if the payment doesn't work

I am waiting to an answer over a week now. Please... really NO ONE has a tip for me????

I found out something. The return url has many parameters:
www.mysite.de/pluginclass?plugin=cbpaidsubscriptions&cbpgacctno=1&cbppdtback=abcd&cbpbasket=30&result=success&cbpid=abcd&tx=abcd&st=Completed&amt=23%2e99&cc=EUR&cm=30&item_number=abcd
For the example now I have replaced some values with "abcd". There is one parameter which caused the problem. The amt parameter. The url without the amt parameter works fine. But when I test the url with this paramter than I was redirected to paypal.

So what is wrong here?

Please help me! I am desperate!

First of all, sorry for our very slow reply here. This topic has been flagged to me several time by the rest of the team, and due to a "human CPU overflow" (aka way too much work for my available 24 hours a day), it got delayed! Sorry about that. Time getting back under control, things should be better now.

There must be a configuration error in your paypal test account settings. E.g. you are forcing a return URL ? The return URL is given by CBSubs's request to paypal and should not be defined in paypal.

Wondering if best and fastest would not be to start with a clean new paypal test account, and follow the Paypal setup chapter in the CBSubs guide step-by-step ?

The guide is here at end:
www.joomlapolis.com/downloads/downloads-single-items/cat_view/118-cbsubs-gpl-download-area
And there is a section 7.4.2 (page 201-210) for paypal setup (you should not setup the paypal encryption described pages 211+, which is not needed in 99.999% of cases given that https is used).

Once that is followed, your paypal setup should work just fine.

IMPORTANT: start from a clean new paypal business test account, as the instructions suppose that unmodified settings are in their default state both at paypal and in CBSubs.

Please reply after that here on how your clean setup is working.

No Problem... I know there are many people with many questions.

I have test it with a new created business account and it works perfect Maybe some preference has caused the problem in the other account. I am very happy now Thank you very much!!!!!