How To Make Relations Between Two Entities From Different Microservices In Spring Boot?

I am trying to make a simple Spring Boot web app using Microservice Architecture.

I have two microservices with entities as defined below:

Microservice 1 :

@Entity
public class Article {

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;

    private String title;

    private String Content;

}

and

Microservice 2 :

@Entity
public class Tag {

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;

    private String title;
}

Now I want to have a Many To Many relation between these two entities in my Gateway.

I had tried to use feign client as below:

Gateway :

@FeignClient(value = "article-service")
public interface ArticleClient {

    @RequestMapping(value = "/articles/", method = RequestMethod.GET)
    Set<Article> getArticleById(@RequestParam("id") Long id);

}

@FeignClient(value = "tag-service")
public interface TagClient {

    @RequestMapping(value = "/tags/", method = RequestMethod.GET)
    Tag getTagById(@RequestParam("id") Long id);

}

And defined Article and Tag entities in my Gateway like this:

Gateway :

@JsonIgnoreProperties(ignoreUnknown = true)
public class Entry {

    private Long id;

    private String title;

    private String Content;

    @ManyToMany(cascade = CascadeType.ALL)
    @JoinTable(name = "article_tag",
        joinColumns = @JoinColumn(name = "article_id", referencedColumnName = "id"),
        inverseJoinColumns = @JoinColumn(name = "tag_id",
                referencedColumnName = "id"))
    private Set<Tag> tags;
}


@JsonIgnoreProperties(ignoreUnknown = true)
public class Tag {
    private Long id;

    private String title;

    @ManyToMany(mappedBy = "tags")
    private Set<Article> articles;
}

I have a table named article_tag in my database (Postgres).

Now how can I define my repositories in the Gateway? How to write getArticlesByTagId() or getTagsByArticleId() functions? I did whatever I could to make this relation work but I think they are not going to get along with each other :)