Update this:
local req_headers = {
['Accept'] = 'application/vnd.twitchtv.v5+json',
}
to
local req_headers = {
['Accept'] = 'application/vnd.twitchtv.v5+json',
['Client-ID'] = 'YOURCLIENTID'
}
Somewhere in your code you are making a request without an attached oAuth and thus are missing a ClientID.