gistfile1.txt

irb(main):022:0> url = 'https://a.b.c:1234/'
=> "https://a.b.c:1234/"
irb(main):023:0> unless url.match(%r{/vco/api$}) ? true : false
irb(main):024:1> url.gsub!(%r{/?$}, '/vco/api')
irb(main):025:1> end
=> "https://a.b.c:1234/vco/api/vco/api"

try %r{\A/.*\z} instead in your gsub

also, use URI.parse and only perform matches on the path to avoid nasty injection vulnerabilities