Help With epin silks PLAYSPAN !

before i buy 50 silks on playspan and i recive a email but i need ask a question:
1- What its the " Serial Number " ?
on the email i recive to codes one like that 111-1111111-11111111 ( i think its the serial number but on the site just need 8 numbers and there are about 15) and other 11a1a11a11a11a11 ( i think its the epin ).
What i need put on the Serial No ?

Ty for all

while charging u need to enter 2 Numbers
1-Epin
2-Serial Number

i know and i know the epin but the serial number need 8 digits and on the email i have 15-16 digits... like that 111-1111111-11111111 the serial

weird oO