Given this:
Then this is definitely wrong:
The error message says as much. getaddrinfo: Name or service not known is a DNS lookup failure; There will never be a hostname like “support.303.303.303.303”.
Where did you get the “support” part from?
The flexify documentation says:
Change S3 endpoint that your application use to
s3.flexify.io(on [sic] another hostname shown in the settings).
So you can’t use the admin console to change it, instead read the topic @falco mentions 
and start with:
DISCOURSE_S3_ENDPOINT: https://s3.flexify.io