You may have had an incident that you needed to report to the regulatory authority.
Following a reported incident, you may have to further explain it by letter or in person during a meeting, or during a follow-up inspection by the regulatory authority.
Perhaps a neighbour has complained directly to you about your operations, and you need to address their concerns, or the neighbour has complained to the regulatory authority, and they have contacted you for an explanation or to have a meeting or to conduct an inspection.
It is possible that a complaint has been lodged without your knowledge or involvement, and the regulatory authority is considering possible charges or orders and wants to conduct an investigation.
Maybe a non-compliance with the terms and conditions of an approval has been noted (self-reported by you or identified during a regulatory inspection), triggering a further inspection, investigation, charges or orders.
You may be ordered to change your operations or the terms and conditions of your approval to operate, and wish to challenge (review or appeal) the order or approval.