Error 11000 Duplicate Key mongoose although not set unique

I make an API in NextJS and use MongoDB Atlas for my cloud database. But I found an error 11000 duplicate key when I create a new role but with the same permissions.resource although I'm not set unique for the field in schema mongoose.

My code like this

// BaseSchema
import { Schema } from 'mongoose';

export class BaseSchema extends Schema {
  constructor(schema: any) {
    super(schema, { timestamps: true });
    this.set('toJSON', {
      virtuals: true,
      versionKey: false,
      transform: (doc, ret) => {
        delete ret._id;
      }
    });
  }
}

RoleModel.ts

const RoleModel = new BaseSchema(
  {
    name: {
      type: String,
      required: true,
      unique: true
    },
    permissions: [
      {
        resource: {
          type: Schema.Types.ObjectId,
          ref: 'Resource',
          required: true
        },
        actions: [
          {
            type: Schema.Types.ObjectId,
            ref: 'ActionMethod',
            required: true
          }
        ]
      }
    ]
  }
);

export interface IRole {
  id: string;
  name: string;
  permissions: [
    {
      resource: string | IResource;
      actions: string[] | IActionMethod[];
    }
  ];
}

interface IModel extends IRole, Document {}

export default mongoose.models.Role || mongoose.model<IModel>('Role', RoleModel);

ResourceModel.ts

const ResourceModel = new BaseSchema(
  {
    name: {
      type: String,
      required: true,
      unique: true
    }
  }
);

// export like RoleModel.ts pattern