Some plugins require native modules to be compiled during installation. To enable this on DSM 7 you will need to install the Entware toolchain and a few packages.

SSH to your NAS, sudo su to root and follow the instructions here:

https://github.com/Entware/Entware/wiki/Install-on-Synology-NAS

After installing Entware and rebooting your NAS, SSH to your NAS again, sudo su to root and run the following command:

opkg install make gcc python3 python3-dev

If your plugin does things with Bluetooth, you may need to install these tools. Using Bluetooth with Homebridge plugins when running on a Synology NAS has not been tested and may not work properly.

opkg install bluez-daemon bluez-libs bluez-utils bluez-utils-extra libudev-zero

Restart the Homebridge package from Package Centre. You should now be able to install plugins that need to compile native modules.