@QFMathew I’ve just discovered another place where “Supplier Reference” crops up, and this time it relates to something I’m finally entering “for real”, following this guide. When it comes to tagging a fee-related debit in the merchant account to a supplier invoice, I have this screen:
This field is limited to 25 characters. Is there any chance of increasing this to 30 characters (like it seems to be in the other New Purchase screen I posted above)? The ref I want to use is actually 27 characters 
BTW it’s possible to add/edit the ref after the event to get the longer length, but IMHO it should be possible to do it at the point of creation, without any discrepancy between the length allowed at creation and subsequently when editing.