Docker Container crashing with extra Arguments

So I'm running into an issue where I'm following an online tutorial from techno dad life:

Everything has gone fine until I run the extra arguments. When I do, I get the error in the screenshots and it erases the entire container if I close it, even if I'm modifying it. I tried both extra arguments for nextcloud and lets encrypt, but both fail.

I'm running OMV4 on a RPi4 (this is one of two). All other containers and instances are working fine, it's just when I try the extra arguments to complete this.

Client: Docker Engine - Community
Version: 19.03.1
API version: 1.40
Go version: go1.12.5
Git commit: 74b1e89
Built: Thu Jul 25 21:35:21 2019
OS/Arch: linux/arm
Experimental: false

OMV Version 4.1.23-1

Thank you for the quick responses.
I added the network through the GUI instead, but the second portion of this build in this for letsencrypt uses the argument:
--cap-add=NET_ADMIN --network my-net

This has the same issue where it errors out and deletes the container. And running the --cap-add=NET_ADMIN by itself also fails. And to be honest, I have no idea what this command is doing.