Unknown command: 'bc'
Hello there!
So I downloaded and installed your plugin but it seems not to work at all. Here the steps I made:
  1. first of all, I didn't changed the *.json file.
  2. I gave me a couple of blood bags and tried to do what you said: "left click with the item in your hotbar selected" but nothing happened. In the context menu I can only drop blood bags.
  3. I tried to invoke the command /bc craft but it output the message "Unknown command: /bc" (of course I have syringes and bandages)
  4. deleted all the files and reinstalled but got the same result aforementioned, without any errors.

(09:08:02) | Unloaded plugin Blood Bags v1.6.1 by Default
(09:08:02) | Loaded plugin Blood Bags v1.6.1 by Default​

This is the json file:

{
  "Blood bags": {
    "Blood bags remove bleeding": false,
    "Can players use the craft command?": true,
    "How many seconds until another bag can be used": 10.0,
    "Instant health to recover": 50.0,
    "Pending health to recover": 50.0
  },
  "Chat prefix": {
    "The chat prefix used for the plugin": "Blood Bags"
  },
  "Crafting": {
    "Amount of item 1 to use": 5,
    "Amount of item 2 to use": 1,
    "First item used for crafting (Item IDs, default value is -2072273936 for bandages)": -2072273936,
    "Second item used for crafting (Item IDs, default value is 1079279582 for med syringes": 1079279582,
    "Time to craft": 30.0
  }
}

Am I doing something wrong?

That's pretty odd, never encountered anything like this before during my testing.

Is this still happening?
I just tested by downloading your update and, alas, still got the same problem.
I checked if all the groups have the permissions to craft them (I have 4 groups on my server) and they have.
Again, I had no error messages in compiling the file on the server.
I gave myself this blood bag
error message

Feel free to ask whatever information you might need.
To use the blood bags, it has to be in the hotbar, I cannot add the button to use it in the context menu when you click on it in the inventory.

Could you DM me the server IP so I could hop on and check?
I was trying to but....
Sorry, recipient(s) empty or do not accept private messages
Not a big issue tho.
 I was hoping the pictures I put on the forum were visible: bandages and syringes were in the hotbar.
http://www.gilmor.it/imago/rust/screenshots/Clipboard99.jpg​

You can connect here:
145.239.188.162:28015

I am inworld right now, when you will be there I will give you the things you need to craft it.

And thank you for your help! :-)