Hi Ravi,
Just letting you know that I have solved this.
It was to do with the config.
FBZP > Pmnt. methods in company code > *select relevant payment method* > Pyt adv. ctrl
Initially this had been set to "restricted to 1 Rows"
I changed it to "as many as req"
After this, the payment advices were spooling.
I assume it has something to do with the number of lines used for the payment advice note.
The payment advice was only generating if the payment advice notes required more than one row.
The payment advice I was initially struggling to generate had only one row.
Thanks!