I just built a number of these monitoring devices and ran into some trouble with setting up mosquitto. Thanks to another user that posted a fix here in Issues, I was able to get my install process down without any errors. Below is my step by step instructions. Hope this helps someone!

#newest version of pi os lite 32 bit from pi imager

sudo apt-get update
sudo apt-get upgrade -y
sudo apt-get dist-upgrade -y
sudo reboot

sudo apt-get install pi-bluetooth

sudo reboot

#get repo key
wget http://repo.mosquitto.org/debian/mosquitto-repo.gpg.key

#add repo
sudo apt-key add mosquitto-repo.gpg.key

#download appropriate lists file
cd /etc/apt/sources.list.d/
sudo wget http://repo.mosquitto.org/debian/mosquitto-buster.list

#update caches and install
sudo apt-cache search mosquitto
sudo apt-get update
sudo apt install mosquitto libwebsockets18=4.2.1-0mosquitto1~buster1
sudo apt-get install -f libmosquitto-dev mosquitto mosquitto-clients libmosquitto1

#install git
cd ~
sudo apt-get install git

#clone this repo
git clone https://github.com/andrewjfreyer/monitor.git

#enter monitor directory
cd monitor/

#(optional) switch to beta branch for latest updates and features (may be unstable)
git checkout beta

sudo apt-get install bluez-hcidump
sudo apt-get install bc
sudo bash monitor.sh

sudo nano mqtt_preferences

sudo nano known_static_addresses

sudo bash monitor.sh

sudo nano behavior_preferences