I am unable to figure exact syntax for mutiselect field to update metadata. When I attempt following then it throws error

await boxService._client.FolderMetadata.UpdateFolderMetadataByIdAsync(folderId: "123", scope: UpdateFolderMetadataByIdScope.Enterprise, 
        templateKey: "arms", requestBody: Array.AsReadOnly(newy] { new UpdateFolderMetadataByIdRequestBody() { Op = UpdateFolderMetadataByIdRequestBodyOpField.Replace, Path = "/doctypes", Value = "e\"test\"]" } }));

Error:

Encountered invalid value for template field key=doctypes

I have no issues in using CreateFolderMetadataByIdAsync though.