Invalid config for [switch.template]: [Receiver-Upstairs] is an invalid option for [switch.template]. Check: switch.template->switches->Receiver-Upstairs. (See ?, line ?). Please check the docs at Template Switch - Home Assistant
Should it be:
“{{ is_state_attr(‘remote.living_room.current_activity’, ‘Listen to Music’) }}”
?
Check the state in the dev tools for the correct entity name
Invalid config for [switch.template]: [Receiver-Upstairs] is an invalid option for [switch.template]. Check: switch.template->switches->Receiver-Upstairs
Where you have ReceiverUpstairs and not Receiver-Upstairs as the log indicates.
Are you sure the log is “up to date”?
With that said AFIK that Key needs to be lower case.
Try this instead: