JPA with "detached entity passed to persist:"

Hello, I have a problem because I use an intermediate table to save the IDs of 2 other tables. I'm not sure what to do with JPA, but I'm not sure what to do, but I'm not sure how to do this.

instance.setDtCriacao(new Date(System.currentTimeMillis()));
instance.setQtMidiaTransmissao(dualListMidias.getTarget().size());
instance = playlistBean.salvarPlaylist(referenceValue);

int i = 1;
for(Midia midias : dualListMidias.getTarget()){             
    MidiaPlaylist midiaPlaylist = new MidiaPlaylist();
    MidiaPlaylistPK midiaPlaylistPK = new MidiaPlaylistPK();
    midiaPlaylistPK.setIdMidia(midias.getIdMidia());
    midiaPlaylistPK.setIdPlaylist(instance.getIdPlaylist());                
    midiaPlaylist.setPk(midiaPlaylistPK);               
    midiaPlaylist.setNrOrdem(i++);
    midiaPlaylist.setMidia(midias); 
    midiaPlaylist.setPlaylist(instance);

    //playlistBean.salvar(midiaPlaylist);
    midiaPlaylistBean.salvar(midiaPlaylist);
}   

Except in the "playlist" table so that I have the ID that I want and the media IDs are already in the dualListMidias.getTarget() list, then I'm going to write all the id.playlist and id.midia in the midiaPlaylist table

My MediaPlaylistBean

@TransactionAttribute(TransactionAttributeType.REQUIRED)
public MidiaPlaylist salvar(MidiaPlaylist entity){
    try{
        entity = super.save(entity);
    }catch(Exception e){
        e.printStackTrace();
    }
    return entity;
}

My MediaPlaylist

@EmbeddedId 
private MidiaPlaylistPK pk = new MidiaPlaylistPK();

public MidiaPlaylist(){
}

@MapsId("idMidia")
@ManyToOne
@JoinColumn(name="id_midia", referencedColumnName="id_midia")
private Midia midia;

@MapsId("idPlaylist")
@ManyToOne
@JoinColumn(name="id_playlist", referencedColumnName="id_playlist")
private Playlist playlist;  

@Column(name="nr_ordem", nullable=false)
private int nrOrdem;


public Midia getMidia() {
    return midia;
}

public void setMidia(Midia midia) {
    this.midia = midia;
}

public Playlist getPlaylist() {
    return playlist;
}

public void setPlaylist(Playlist playlist) {
    this.playlist = playlist;
}

public void setPk(MidiaPlaylistPK id) {
    this.pk = id;
}

public MidiaPlaylistPK getPk() {
    return this.pk;
}

public void setNrOrdem(int nrOrdem){
    this.nrOrdem = nrOrdem;
}

public int getNrOrdem(){
    return this.nrOrdem;
}

Playlist.java

@Id
@GeneratedValue
@Column(name="id_playlist")
private Long idPlaylist;

@OneToMany(mappedBy = "playlist", fetch=FetchType.LAZY)
private List<MidiaPlaylist> midiaPlaylist;

public List<MidiaPlaylist> getMidiaPlaylist(){
    return midiaPlaylist;
}

public void setMidiaPlaylist(List<MidiaPlaylist> midiaPlaylist){
    this.midiaPlaylist = midiaPlaylist;
}

public Playlist() {
}   

public Long getIdPlaylist() {
    return this.idPlaylist;
}

public void setIdPlaylist(Long idPlaylist) {
    this.idPlaylist = idPlaylist;
}

The error is :

  

detached entity passed to persist: com.bcm.midia.database.entity.Midia

Where I think the error is : in Midia mapping

@Id
@GeneratedValue
@Column(name="id_midia")
private Long idMidia; 

@OneToMany(mappedBy = "midia", fetch = FetchType.LAZY, cascade=CascadeType.MERGE)   
private List<MidiaPlaylist> midiaPlaylist;

Can anyone explain to me why I can not just save in the MidiaPlaylist table from this many-to-many mapping form?