Advancement for renaming an entity to grumm/dinnerbone

so I want to create an advancement for renaming an entity into grumm or dinnerbone and I cant figure out how to do so. Ive tried this:
{
  "parent": "skyquest:story/what_is_broken_can_be_reforged",
  "display": {
    "icon": {
      "id": "minecraft:name_tag",
      "count": 1
    },
    "title": "Huh?!",
    "description": "???",
    "frame": "goal",
    "show_toast": true,
    "announce_to_chat": true
  },
  "criteria": {
    "rename_entity_to_grumm": {
      "trigger": "minecraft:player_interacted_with_entity",
      "conditions": {
        "entity": {
          "nbt": "{CustomName:\"Grumm\"}"
        }    
      }
    }
  },
  "rewards": {
    "function": "skyquest:give/loot/advancement/story/huh"
  }
}

and I tried changing the format of nbt into many ways. for example:

{CustomName:Grumm}
{CustomName:"{\"text\":\"Grumm\"}"}
{CustomName:'{"text":"Grumm"}'}
{CustomName:'Grumm'}
none of that worked. I also tried to replace 1 slash with 3 slashes (which I put in the commands above but discord only shows one of 3)