We are asking for these two bits of information from you for two reasons:

We need to know the Pro#, or Freight Bill number, so we know what invoice you are paying.

We are asking for your account number as an simple added level of security.  Anyone
can type any freight bill number they want.  It is doubtful that someone will want
to pay your invoices for you.  However, if the account number is entered and it
matches the number that is on your invoice in our system, then we can assume that
the invoice belongs to you.  Few people would have access to your invoices and know
your account number.  You are not just some random person playing around,
entering data randomly on websites.

Thank you for your cooperation.  We hope this added step is not an inconvenience.