Hi,
You can find this REP in the CH database / included in the CH license
Local CH objects can be found in the 11500..11599 no.range and in the 3010530.. no ranges
If I'm not mistaken this object numbering is from old NAV days.
I just checked this for NAV 2018 CU29
It was some kind of addition to the sales invoice, used to share a unique payment reference number
ESR stands for the Swiss German term "Einzahlungsschein mit Referenznummer"