If you're not pairing it through the menu: settings> remote> pair remote>
Then try pairing with power unplugged from the roku, have the remote ready with battery door off, plug the roku in, when the roku starts bouncing start pressing and holding the pairing key, when the roku stops bouncing, release the pairing key for sec and start pressing again until you get confirmation its paired.
If you need a new remote you can get them at Walmart or Best Buy and Amazon for $19.88, its RC-AL7R remote.
It uses the same type of remote wifi-direct as the roku. You have vudu library, no vudu app on fire stick. You have big amazon library of movies and tv, with fire stick both movies and tv are on one line intermixed with each other. Amazon Sticks suck.
Can you please provide the model numbers of the device?
You'll want to start here to troubleshoot issues with your wireless remote: How do I set up my Roku® enhanced "point-anywhere" remote?
Restarting your Roku device, and your wireless router/modem is a great first step. Replacing the batteries in your remote can help. Changing the wireless broadcast channel on your wireless router, to one that isn't in use by another nearby wireless network, can reduce wireless interference and be extremely effective in improving remote functionality.