The documentation says proxyname/1 returns proxy_protocol_info(), it actually returns:
{ok,{{inet:ip_address(), inet:port_number()}, {inet:ip_address(), inet:port_number()}}}
Looking at the code, looks like the code is wrong (spec at the function matches the docs, but proxy_opts() is what is wanted), problem is to fix this would break backwards compatiblity.
Maybe a new function, or just amend the docs and drop proxy_protocol_info()/proxy_opts()` altogether?