Error code 126 is a fraud protection alert. Below is the definition by Payflow Pro:
Fraud Protection Services Filter — Flagged for review by filters
Important Note: Result code 126 indicates that a transaction triggered a fraud filter.
This is not an error, but a notice that the transaction is in a review status. The transaction has been authorized but requires you to review and to manually accept the transaction before it will be allowed to settle.
Result code 126 is intended to give you an idea of the kind of transaction that is considered suspicious to enable you to evaluate whether you can benefit from using the Fraud Protection Services.
To eliminate result 126, turn the filters off.
For more information, see the Fraud Protection Services documentation for your payments solution. It is available on the PayPal Manager Documentation page.
The Payflow Pro guide for users can be accessed using the link below (go to Chapter 4 to see the definition of error codes):