Let's take a look at the error message:
ERROR: XLSX file does not exist -> /config/Lev1/SASApp/C:\Users\me\Documents//Transactions.xlsx
Look at the file path.
/config/Lev1/SASApp/
is clearly a path on a Linux/Unix server. This is the default location when running a Workspace server. From this, I will guess you connected to SAS through Enterprise Guide (EG).
C:\Users\me\Documents//Transactions.xlsx
This is the path you entered.
So what happened? SAS is running on a remote server -- a server running Linux/UNIX. You asked SAS to open "C:\Users\me\Documents//Transactions.xlsx".
However, "C:\stuff\more\file" is not a valid filesystem path on Linux/UNIX. So SAS assumed this was the file name and looked for it in the default location "/config/Lev1/SASApp"
To fix this, you need to upload your XLSX file to the server. Then use the path to the file on the server in your code. Talk to your system admin if you are unsure how to do this.
Alternatively, you can use the Data Import Wizard in EG. I'm not a fan of it as it screws things up at times, but it does work.