Is it possible to set a weak reference through a mutation in Sanity.io?

mutation = {
            mutations: [
                {
                    create: {
                        _id: crypto.randomUUID(),
                        _type: "team",
                        title: team.name,
                        badgeUrl: team.logo,
                        footballApiId: team.id,
                        isNationalTeam: team.national,
                        country: {
                            _type: 'reference',
                            weak: true,
                            _ref: sanityCountry._id
                        },
                        slug: {
                            type: '_slug',
                            current: slugify(`${team.id}-${team.name}`)
                        }
                    }
                }
            ]

ERROR TypeError: Cannot read properties of undefined (reading '0')