FYI, trying via wget shows same issue:
[~] # wget https://getchannels.com/dvr/setup.sh
--2021-10-07 15:34:53-- https://getchannels.com/dvr/setup.sh
Resolving getchannels.com... 185.199.109.153, 185.199.110.153, 185.199.108.153, ...
Connecting to getchannels.com|185.199.109.153|:443... connected.
ERROR: cannot verify getchannels.com's certificate, issued by ‘CN=R3,O=Let's Encrypt,C=US’:
Issued certificate has expired.
To connect to getchannels.com insecurely, use `--no-check-certificate'.
The last line seems to indicate you might be able to bypass the cert check, though usually not recommended, and unsure what further steps you'd need to take to complete install after that.