@baris
thx a lot ！！！！
it's work finally！

@baris thx for ur reply
but i used

/api/topic/782?page=1

and

/api/topic/782?page=2

then i get the result of "posts" are same (last 20 posts)

this is page 1

this is page 2

there is same pid in the posts array

I use

/api/topic/${tid}/${postIndex}

to get data of topic.
BUT the result of posts are limit in 20.
How can I get all topic of post with api.

BTW I know the way that

/api/user/${userslug}/topics?page=x

to get all topics of category ,
but it's not work in

/api/topic/${tid}/${postIndex}

someone help me plz