In case the AutoReply stop after some time, make sure to disable the energy save for this app in your device (application) setting. (Especially Xiaomi and Huawei devices; Xiomi devices also enable "Autostart" for this application.)

Turn OFF and ON Auto Reply in the notification access list screen.

For the batter, understanding please check the link https://dontkillmyapp.com and find your device name and follow all the steps by step instruction.