I have been a long time Roku user and I bought an express streamer for my office tv about 2years ago. In that 2 years I have had to replace the remote 3 times because it would stop working. Wouldn’t pair or connect. Not damaged, just stopped.
Please reply here with the serial number of the Roku device associated with the affected remote. It can be found at the back or underneath the player itself. I'll be able to further assist you from there.