Hi Barbara,
I'm pretty sure I used it several times to get the for-period in thus making retro-postings more transparent - and it worked. But it's somem time ago and I don't currently have access to those systems.
So, a few options to try:
you are referring to a customer exit. There's now also a BAdI available: SMOD_PCPO0001. Maybe you try that one. Very similar options. Maybe you can try that one.
The exit as well as the BAdI have a method ending in ...001 for the whole line item with all fields (incl. teh text) and one ...002 for the TExt and an assignment number specifically. I seem to remember that, when I used it, I used the first one, because I was manipulating something else at the same time. the relevant field for you SGTXT is available for output in both cases. So, I've never seen ...0002 working. Maybe the "Big" one is the one to go for.
Otherwise: check with your FI experts, whether there may be something in their config not allowing, what you are trying to do. Maybe the text is too long? That could explain why it's only working in simulation, because most, but not all errors pop up in the simu.
Sorry I can't just grab what I've done earlier and have to guess around a bit, but I hope it might be helpful any way.
best wishes from London
Sven