Is there a way to make this a free option instead of having to pay using scraps/rp?

im an idiot

Glad you figured it out :)

i would like to know plz how to make it free

There are two ways to make it free.

The first option is to set the default hourly building cost, default hourly base cost, and default structure damage cost to 0. Your config under Cost settings should look like this:

  "Cost settings": {
    "Material cost multipliers": {
      "twig": 1.0,
      "wood": 1.0,
      "stone": 1.0,
      "metal": 1.0,
      "armored": 1.0
    },
    "Default hourly building cost": 0,
    "Default hourly base cost": 0,
    "Default structure damage cost": 0​

The second option would be to make a protection level with its own cost settings. This would be if you want some people to have to pay, but others to have it for free. It would look like this:

  "Protection settings": {
    "Protection levels": {
      "0": {
        "Online protection percentage (0-100)": 100.0,
        "Offline protection percentage (0-100)": 100.0
      },
      "1": {
         "Online protection percentage (0-100)": 100.0,
         "Offline protection percentage (0-100)": 100.0,
         "Hourly building cost" : 0,
         "Hourly base cost" : 0,
          "Cost per damage": 0
      }
    },

With this second option, level 1 protection will be free but level 0 will cost whatever is set in the default cost settings.

Oozle30 i not recomend you to do free upkeep
1 reason players before leave server can grief other players bases. And those unlucky players have trouble
2 reason no one knows how active players is, so those inactive bases cant be raided for ages
SOLUTION make 20 scrap per hour... its = 2 days offline with 1000k scrap in tc (its not to cheap and not to expensive)

As Soon as you make any changes to config file even 1 number you get error in console 

All i changed was this 

"Default hourly building cost": 0.0,
"Default hourly base cost": 0.0,
"Default structure damage cost": 0.0

made the cost 0.

now get 

Can you post your full config, good chance that something is missing somewhere.

{
"General settings": {
"Currency item ID (if not using economics)": -932201673,
"Use economics balance (requires economics plugin)": false,
"Use reward points (requires server rewards plugin)": false
},
"Protection settings": {
"Protection levels": {
"0": {
"Online protection percentage (0-100)": 100.0,
"Offline protection percentage (0-100)": 100.0
}
},
"Delay after taking damage (seconds)": 10,
"Delay for offline protection (seconds)": 600,
"Protect buildings and deployables (true/false)": true,
"Protect players (true/false)": true,
"Protect vehicles and horses (true/false)": true,
"Protect traps and electronics (true/false)": true
},
"Cost settings": {
"Material cost multipliers": {
"twig": 1.0,
"wood": 1.0,
"stone": 1.0,
"metal": 1.0,
"armored": 1.0
},
"Default hourly building cost": 0.0,
"Default hourly base cost": 0.0,
"Default structure damage cost": 0.0
},
"Indicator settings": {
"Enabled": true,
"Persistent": false,
"Image url": "https://i.imgur.com/ue05FGg.png"
}
}

There you go mate

Config looks good, wasn't able to reproduce it on my server. Made some changes in v2.1.4 that might help though, give it a try.

No still the same as soon as you try make it free or cost no resources you get the error

Merged post

Even delete the mod then re upload to server and just change to use server rewards instead of scrap and its broken again 

Try deleting the CupboardBalances.json in */oxide/data. Thats my best guess at the moment.

This issue still persist, I uploaded the plugin for the first time, changed the config and reloaded, get the same error as the guy above. I thought the exact same thing you are suggesting. That I messed something up in the config, but re-uploading the default vanilla config will still yield an error on reload.