A component of spend management setup is ensuring that the user can submit personal cash/out-of-pocket expenses. As an Admin, you are able to control which users are able to create new out of pocket cash expenses.
When a user does not have this enabled for their account, they will see see this note within the spend module:
Managing personal cash / out-of-pocket expense authorisation
Step 1: Click on Settings
Step 2: Click on Payment Methods
Step 3: Hover your mouse over the Out of pocket line. Click on the clipboard icon (Authorized users for Personal Cash). This will open the authorize user edit panel
Step 4: Select individual users or bulk select. (For bulk select, tick the box on the top line in front of Display name