So what I did was find the files in notepad++ that contained the phrase voucher number and replaced the word voucher with PO so now it reads PO Number and provides sequential numbering.

erp\modules\accounting\includes\views\expense\payment-voucher-single.php
Line 49: printf( __( ‘Voucher Number: %s‘, ‘erp’ ), $transaction->id );

and

erp\modules\accounting\includes\views\expense\payment-voucher-single.php
Line 9533: msgid “Voucher Number: %s”

Wish I was able to start the voucher numbering at a higher number than numeral 1
Like 100254 or something