Instant Invoice Error: 'Length of Payment reference cannot exceed 26 for Swiss Invoice 27 Modula 10'

When trying to create an instant invoice for a Swiss company using Swiss Invoice 27 Modula 10 we get presented with the below error:
 

Can anyone advise where IFS is trying to pull/create this payment reference from so we can ascertain why it is the wrong length. Is there some other set up we need to do for this?

Thanks