Good day, depending on your version and patch level there are a couple of entry points your can use to facilitate this, I had personally used BEFWRIDAE in SUBGAS, but not you have to test reversal status and also will have to read the original line record as the reversal creation process works very different to the standard GAS object record creation. 

Good day, depending on your version and patch level there are a couple of entry points your can use to facilitate this, I had personally used BEFWRIDAE in SUBGAS, but not you have to test reversal status and also will have to read the original line record as the reversal creation process works very different to the standard GAS object record creation. 

Thanks for the above response, is it above entry point will work for X3V12 Patch 27 [2021 R3 (12.0.27)]

Good day Shamee, yes that entry point has been in X3 for a while and most definitely in 2021R3.