A permission is not an appointment

You can see the governance screens and LEAT still refuses you. This
page explains why, because it looks like a bug and it is the control
working.

The mistake

Somebody grants you the "Governance & board" permission. You open the
appointments register, find the person you need to appoint, and LEAT
refuses.

The permission opens the screen. It does not make you anybody.

Why they are separate

Because a screen is granted by an administrator and an office is
granted by the board.

If the two were the same thing, anybody who could edit a user account
could hand themselves the power to appoint trustees. That is one form
submission away from controlling the organisation, and it is the exact
failure this separation exists to stop.

What actually gives you authority

An appointment. It names four things and it needs all four:

1. An office. A seat that exists, created by a clause of a governing instrument.
2. A capacity. Which hat you are wearing. The same person can be a trustee and the Finance Director, and the two have different authority.
3. A scope. Which entity, programme or grant it reaches. ALL is allowed and it is a decision, not a default.
4. An expiry. Every appointment ends. There is no indefinite option.

What to do

Ask whoever holds the power to appoint. LEAT will tell you how many
people hold it, though not who they are — a refusal that named names
would turn a control into a list of who might do you a favour.

A note on job titles

Being the Finance Director in the HR record is not an appointment
either. Nor is being an administrator, being senior, or being in the
right department. Every one of those is somebody else's record of
something else.