As of API version 2026-10, the static session.currentSession.staffMemberId field has been removed from the POS UI Extensions Session API. It was deprecated in 2026-07 in favour of session.staffMember, a reactive signal that updates when a different staff member pins into POS.
Before targeting API version 2026-10, replace reads of session.currentSession.staffMemberId with session.staffMember.value?.id. To react to staff changes while your extension is running, subscribe to the signal with session.staffMember.subscribe((staffMember) => { ... }), or read .value during render in a Preact component with @shopify/ui-extensions/preact imported to re-render automatically.
Extensions on 2026-07 and earlier are unaffected. The BaseData session.staffMemberId available to receipt targets is a separate API and is unchanged.
https://shopify.dev/docs/api/pos-ui-extensions/2026-10/apis/session-api