The accountant role is for people who need access to accounting, expense, and incoming-invoice information across the band.
When musician invoices are enabled, accountants can prepare fee and travel-expense suggestions, save private intermediate states, release the accounting to confirmed musicians, and track received and paid invoices. A played gig has a dedicated Accounting tab; the regular gig page stays form-free.
The same person may handle booking and accounting, but the booker role alone does not grant access to prepared amounts. Add the accountant role to that person's band membership, or use an administrator account.
Musicians can enter their own expenses, but they cannot see other people's expenses.