Edit: apparently the first time you claim a Steam key on Itch.io it has to verify that you have a Steam account. After this it will just directly give you the key. The interface for this verification was temporarily broken, but has been fixed by Itch.io.
On your download page on itch.io there should be a link to "Claim Steam Key". Clicking it should give you a key (a 15 digit string), this link should not take you to any other website.
You can then copy that key, open the Steam client. Go to the Games menu at the top of the window and select "Activate a Product on Steam..." where you can paste that key.
I believe you can only activate a Steam key through the client application. There is no way I know of to do it through Steam's website. I'm not sure what link would take you there, or why?
Itch.io has some official instructions here:
https://itch.io/docs/buying/already-bought
If that doesn't work, you can let me know but if there's a problem with itch.io or Steam's services I don't have a lot of control over that, we may have to contact their support. Sorry about the inconvenience.
You can activate a steam key via https://store.steampowered.com/account/registerkey. No need to start the Steam client.
I can do a screen cap video, if it would help, but when I click on "Claim Steam Key" it opens a web page with steam, tells me to sign in, or if I'm signed in, to click to accept the terms. Then when I do, it brings me back to itch, then says failed. You know what? I'll show you... I'm a bit swamped but I'll record the process this weekend.
-LeRoy3rd
I've also email support at itch.io.
Sorry there's no sound, it's noisy where I live. It seems like the Steam Key process has changed significantly. Now you click a link and are re-routed to Steam's web page. It doesn't matter if I'm on my desktop, laptop, phone, or tablet, the result is always the same. It says it fails to connect to Steam. I've also tried being signed into or NOT being signed into Steam when I start (the difference being, if I'm not signed in, it asks me to, then everything is the same). I've also tried having the Steam client open on my computer, it still opens Steam's web page, and everything else is the same. I've also checked my Steam account to make sure Lizard wasn't added, it wasn't.
If it was just a matter of copy/pasting a key, I would have been done in a couple of seconds. I mean, I've got hundreds of titles on Steam, and am a pro of GoG and HumbleBundle... Key pasting isn't exactly a barrier for me these days. Anyway, here's the video that shows the current (completely broken) process for getting the included Steam key:
-LeRoy3rd
Thanks for clarifying what you're seeing. That process looks new to me, and I really don't understand why a connection to Steam has to be made. When I've claimed keys in the past on other games it was just a simple click that reveals the text of a key, unless I'm not remembering correctly. I gave keys to itch.io and they should be able to give them directly to you. :( I will contact support. I'm sorry this has happened.
