Why am i unable to use 'Project Type' as a source in accounting rules for payables?

Summary:

As per this document:

Fusion: What Subledger Accounting Sources Are Available For Fusion Payables? (Doc ID 2628556.1)

'Project Type' is listed as one of the sources that is available in payables invoices.

But whenever I am putting the project type and validating I am getting a validation error:

Why is this happening?

Thanks

Atul