Well, I'm still new to the dev staff, but I'm guessing since the cash system is improved, the donating feature was removed. I'm not very sure though.
I think you can still use the old file, but it probably need some modification to work correctly.
Well the old cash mod was developed by Cybertrash/Seapyramid. It did have a donate/send cash system, even though it was not quite noticeable. The new cash script was made by Arianna, it seems that she did not add an equivalent donate/send money system. It can be added in future, the old cash system was quite glitchy though since you can technically send negative amount of money to other users and thus 'steal' money from them.
Well I didnt test it myself, but the old trade script had this problem when you send cash to friends. Thus I am assuming the glitch may be present here too.