You Can't decrypt MD5
The link you mentioned it only decrypt MD5 which you encrypt there or someone else did
You try This String
a23ee3caaeef2cf08e96dde037a74df4
It will not decrypt but once you encrypt the original data it will decrypt data
you can try with this original data string as below
amount=1¤cy=USD&fields=id,amount,notify_status,currency,time,reference,notify_id&id=3ea3b468735b81e1ef5536d91¬ify_id=D0000036689-e915dc40b72c89e4ed55¬ify_status=success&reference=190404184802PTM03498&time=20190404104820&token=AC12A68A47E1D4569A98688062F9860D0