Someone with the Buyer role opens Create Order and the Procurement BU field has nothing to choose. The role alone is not enough: Fusion also needs the person set up as a procurement agent for that business unit.
Procurement access is granted per business unit. Oracle describes procurement agents as users with roles such as buyer who are defined as agents, and enabled for one or more procurement actions in each procurement BU. A user with the Buyer role but no procurement agent record for the BU has no BU to pick.
My Oracle Support notes, for readers with access. We do not reproduce their content.
Sources Written in plain words from Oracle’s public documentation and the support notes and forum reports listed above. Not yet checked against a live instance by our reviewer. Navigation and behavior vary by configuration; verify in your own instance and test before acting.