Using P417M MultiBank Feature

Hello,

Looking at assigning  multiple bank accounts for suppliers:

From the documentation and also Document 2301729.1, I can see that we can set up more than 1 supplier's bank account using a combination of record type and G/L account. But also the G/L Account code on this set up (P417M) is optional. If it were optional how would the voucher be targeted towards the correct supplier bank account if the user does not enter the G/L Code  when creating the voucher?

thanks