Port 80 seems to be blocked for api.benjune.com. I don't have any experience with Caddy, but that would block the http-01 challenge. Maybe try opening port 80? (I thought Caddy was also supposed to be able to do the tls-alpn-01 challenge on port 443, but apparently that doesn't work.. Maybe you configured Caddy to only use the http-01 challenge? 
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