Oh that is awful. It seems like they should inquire into the bag you are trying to attach a strap to ensure it is compatible.
That is really terrible. The sales folks should be aware that these additional straps are intended to fit only specific styles since that now seems to be the case. I don’t think many are aware because from what I’ve heard, these straps have been marketed as being for all bags with a shoulder strap loop. I’m so sorry for your inconvenience and disappointment.