Failed to call hook 'API_SendTextMessage' on plugin 'DiscordMessages v2.1.2' (NullReferenceException: Object reference not set to an instance of an object)
  at Oxide.Plugins.DiscordMessages+FancyMessage.ToJson () [0x00000] in <c14d50fe7b5b4e1f8035b0b6fd117f45>:0 
  at Oxide.Plugins.DiscordMessages+Request..ctor (System.String url, Oxide.Plugins.DiscordMessages+FancyMessage message, Oxide.Core.Plugins.Plugin plugin) [0x0000d] in <c14d50fe7b5b4e1f8035b0b6fd117f45>:0 
  at Oxide.Plugins.DiscordMessages+Request.Send (System.String url, Oxide.Plugins.DiscordMessages+FancyMessage message, Oxide.Core.Plugins.Plugin plugin) [0x00000] in <c14d50fe7b5b4e1f8035b0b6fd117f45>:0 
  at Oxide.Plugins.DiscordMessages.API_SendTextMessage (System.String webhookUrl, System.String content, System.Boolean tts, Oxide.Core.Plugins.Plugin plugin) [0x00012] in <c14d50fe7b5b4e1f8035b0b6fd117f45>:0 
  at Oxide.Plugins.DiscordMessages.DirectCallHook (System.String name, System.Object& ret, System.Object[] args) [0x00c12] in <c14d50fe7b5b4e1f8035b0b6fd117f45>:0 
  at Oxide.Plugins.CSharpPlugin.InvokeMethod (Oxide.Core.Plugins.HookMethod method, System.Object[] args) [0x00079] in <9affce1cd15c4ec183941adef8db1722>:0 
  at Oxide.Core.Plugins.CSPlugin.OnCallHook (System.String name, System.Object[] args) [0x000d8] in <4452f821def6406d834e4149849fe7ea>:0 
  at Oxide.Core.Plugins.Plugin.CallHook (System.String hook, System.Object[] args) [0x00060] in <4452f821def6406d834e4149849fe7ea>:0

When I activate the option Send the information of the sales machines I get this error .., help!

This json file:

{
  "Chat Settings": {
    "ChatColor": "#b7f5ff",
    "Prefix": "[NTD] :",
    "PrefixColor": "#42d7f4"
  },
  "Discord Settings": {
    "BotToken": "0",
    "ChannelID": "0"
  },
  "Discord Webhook": {
    "URL from your Discord channel": "https://discordapp.com/api/webhooks/667460816785768448/Ewfm49r1Me3y86v-ISNYOJPXAi_OIvZBAQil27W0ZRr0rnjZBojMOQr_PjHVtKcxRh7z",
    "Use WebHook via DicordMessages plugin dependency": true
  },
  "NOTIFY -=- ADMIN": {
    "Group granted permission": false,
    "Group revoked permission": false,
    "Player Banned": false,
    "Player Kicked": false,
    "Player Unbanned": true,
    "User granted permission": false,
    "User revoked permission": false
  },
  "NOTIFY -=- BOTS -=- APC/NPC": {
    "BRADLEY APC on hunt": false
  },
  "NOTIFY -=- HACK VIOLATION": {
    "Player Hack Violation": false
  },
  "NOTIFY -=- MESSAGES -=- PLAYER/SERVER": {
    "On Player Chat message": false,
    "On Server message": false
  },
  "NOTIFY -=- PLANE/HELI": {
    "airdrop": false,
    "CH47 has been killed": false,
    "CH47 is under attack": false,
    "Hack of Crate has ended": false,
    "Hack of Crate has started": false,
    "Hackable Crate Dropped": false
  },
  "NOTIFY -=- PLAYER -=- ACTIONS/ENTITY": {
    "codelock change": false,
    "Player has dismounted": false,
    "Player is trying to dismount": false,
    "Player is trying to mount": false,
    "Player tries to unlock": false,
    "Players has mounted": false
  },
  "NOTIFY -=- PLAYER -=- CONNECT/SPAWN/SLEEP": {
    "Player has Connected": false,
    "Player has Disconnected": true,
    "Player Respawn": false,
    "Player Respawned": false,
    "Player Sleep Ended": false,
    "Player Sleep Started": false,
    "Player Spawn": false
  },
  "NOTIFY -=- PLAYER -=- ELSE": {
    "Player is speaking in a microphone": false,
    "Player updated name": false
  },
  "NOTIFY -=- PLAYER -=- FIGHT": {
    "Player is attacking": false
  },
  "NOTIFY -=- PLAYER -=- HEALTH/KILL/DEMOLISH": {
    "Player demolishing entity": false,
    "Player Die": false,
    "Player wounded": false
  },
  "NOTIFY -=- PLAYER -=- LOOT": {
    "Player is looting item": false,
    "Player Loot Entity": false,
    "Player Loot Player": false
  },
  "NOTIFY -=- SERVER -=- PLUGIN": {
    "Plugin Loaded": false,
    "Plugin Unloaded": false,
    "RCon Command": true,
    "RCon Connection": true,
    "Server Save": false
  },
  "NOTIFY -=- SHOP -=- BONUS": {
    "a door has been knocked": false,
    "a Player is accessing a mailbox": false,
    "New sell offer added in VendingMachine": true,
    "Player customer has complete a shop trade": true,
    "player receive bonus item": false,
    "player start a oven": false,
    "player update a sign": false
  },
  "NOTIFY -=- SPECTATE": {
    "Player Spectate": false,
    "Player Spectate End": false
  },
  "NOTIFY BONUS -=- ONLINE PLAYERS REPORTER -=-": {
    "Report online players count; refresh on players connections and every 15min": false
  },
  "NOTIFY DANGEROUS TREASURES -=- MESSAGE -=-": {
    "DangerousTreasures message to player": false
  },
  "NOTIFY EXTENDED -=- BOTS -=- APC/NPC": {
    "NPC is attacking entity": false
  },
  "NOTIFY EXTENDED -=- HELI/PLANE -=- ": {
    "Chinook spawned": false,
    "Helicopter spawned": false
  },
  "NOTIFY EXTENDED -=- PLAYER -=- MISC & ROLEPLAY": {
    "NPC is attacking entity": false,
    "player received a snapshot": false
  },
  "NOTIFY EXTENDED -=- VEHICLE -=- ": {
    "Player using car": false
  },
  "PLAYER -=- ACTIONS/ENTITY": {
    "code entered": false
  },
  "Settings": {
    "SteamIDIcon": "76561198044414155"
  }
}

I'm not able to reproduce this or see any issue there.