What is the best way to prevent direct GL Accounts from being used on non-project (e.g. "X") transactions?

There’s nothing “out of the box” to control this as not all sites use projects and some companies use both projects and other ways to track revenue and direct expenses so there’s not a clear-cut right or wrong way to do this.  A few things that we have used over time and at different sites:

• Approval Maps on invoices and expense receipts to send things for an additional approval if an unexpected or undesired combination is used
• Clear differentiation between Overhead and Direct non-stock items
• Customizations with either warnings or errors for certain combinations of accounts / projects

Hey ​@Bob Stewart 

One option is to use account class or subaccount restrictions so that COGS accounts are primarily available only through inventory transactions or project-related processes rather than manual entry.

Another approach is to use a validation rule or customization that checks whether the account being used belongs to an account group intended for projects and blocks it when the project is “X.”

Let me know if this helps