There are too many old references to how to use Ruby's Net::HTTP to do SSL, post JSON, etc., so here is a simple, fairly modern example for future reference, posting a JSON-RPC call.

net_http_ssl_json_post_request.rb

require "json"
require "net/http"

url = "https://mainnet.era.zksync.io"
pp JSON.parse(Net::HTTP.post(URI.parse(url), {"method": "eth_blockNumber", "params": [], "id":1, "jsonrpc":"2.0"}.to_json, "Content-Type" => "application/json").body)

# => {"jsonrpc"=>"2.0", "result"=>"0x22d9d5d", "id"=>1}