PayPal Security header is not valid

I ma getting the common "Security header is not valid" 10002 error code when trying to checkout with Paypal Payments Pro. This is a new site that is about to launch. I believe I have read every thread on the internet about this, and have gone through every "fix" and nothing has worked.

1. I am using live API credentials. I don't have a sandbox account so I am not using sandbox credentials. Also, eCart (6.08) is NOT toggled to "sandbox."
2. I have recreated my API's with PayPal, 4 times so this is not just a bad API. And, each time when I created the API's, I clicked that I accepted the agreement.
3. I cut and paste the API username, API password, and API Signature, and there are absolutely no leading or trailing spaces or missing characters.
4. I am using the correct credentials. I found a method for verifying with PayPal if the credentials are valid by populating a URL with the credentials. They are indeed valid and I am using the API credentials and not my PayPal account credentials.
5. I have recreated the ecart files using the checkout wizard twice, just to be on the safe side.
6. I am using SSL just in case is matters.

I have done everything I can thing of and have been up all night trying to figure this out. I am at my whits end. What could possibly be going wrong? I would really appreciate your help.

I'll need to troubleshoot directly, see the private message section.

See private message.

Ok, So it works when using PayPal express checkout without giving the error, it;s only a problem on using a Credit Card.

Seams like the credentials are not valid for PayPal Direct Checkout, only valid for Express Checkout.

It looks like you need to upgrade to a pay[pal payments pro account, contact Paypal for details.

Jason, I just got off of the phone with PayPal. I was escalated up to someone that seemed to understand the issue. They are telling me that the PaypPal Payments Pro is active and the specific error message I am receiving means that the credentials are wrong or are being submitted incorrectly from the shoppping cart. I am confident the credentials are correct, and as you discovered earlier, you could use them in PayPal Express Checkout....so they are clearly not wrong. They want me to submit a Correlation ID so they can see what string was submitted but this will take a minimum of 24 hours up to 72 hours to address, which is time I don't have. How can I output the string?

<?php echo(PP_DirectPayment_Result("Full Request")) ?> shows me a long string (see private), but he said this is not a valid string as there are no ampersands. I assume this is not meant to show the actual URL string. Do you have any other suggests?

After another call with PayPal, I got a tech that had been there long enough to know the evolution of their products. I was told that I am using Payments PayFlow Pro... and they are now referring to it as "Payments Pro" and and phasing out the old Payments Pro that used the API's. I even have a welcome letter from a few months ago where PayPal welcomed my client to "PayPal Payments Pro" even though we were using "PayPal PayFlow Pro." Changing the webassist settings to PayPal PayFlow Pro in webassist and using the merchant login information did the trick. Maybe I should have known this...but I can't imagine why. Anyway, I hope this helps someone else out.

FYI - Another clue was in PayPal where you create your API credentials. It used to say something about creating credentials for shopping carts and third party solutions. It now says, "Manage API credentials to integrate PayPal Express Checkout." No mention of Payments Pro or other PayPal products.

Ok, Glad to hear you have it working.