Problem:

When transaction numbers are generated, they do not appear to have the correct ASEC digits at the beginning of the transaction number. It appears that they are using a different ASEC number.

Solution:

With auto transaction numbers  - uses the ASEC + file number padded to 8 digits (left padded with zeroes) + check digit. 

If the importer has an ASEC set in their profile - Customs section, that takes precedence over the brokers ASEC number.