D365FO debugging

Hi,

I'm trying to debug a development environment (demo - 7.3, Update 12) and have tried the following methods, all unsuccessfully:

1. Open VS as admin, find code, add breakpoint, Debug > Attach to process (w3wp.exe)
2. Open VS as admin, set startup project and object, Debug >Start debugging
3. Unticked the "Load symbols only for items in the solution" under Dynamics 365 > Options

I'm trying to debug a vendor payment file (Payment Journal > Generate payments). The file gets created, but I can't step into any code. I am logged into both VS and D365 for Finance and Operations with the same username/account.

Can anyone give any more suggestions/fixes?