Firewalld with variable source

I placed a comment earlier but this is more of a bash expansion issue. So the proper way would be to use a loop and split subnets by ,

#!/usr/bin/env bash

read_file=$(curl -s https://file.test.com/tips | sed 's/[{}]//g')

saveIFS=$IFS

IFS=',' read -ra subnets <<< "$read_file"

for subnet in "${subnets[@]}"
  do
    firewall-cmd --zone=trusted --add-source="$subnet" --permanent
  done 

firewall-cmd --reload

IFS=$saveIFS

Or the other alternative is using eval or even printf '%q' "${subnet}"

Using eval which isn't recommended but is fairly secure for what you want.

eval firewall-cmd --permanent --zone=trusted --add-source="$(curl -s https://file.test.com/tips)" && firewall-cmd --reload