Add relation one to Many

Hi, i am using rest API to add child objectId to my table, relation is 1:n, but after use API, new child objectId replace last one and every time table row has one related child. was i clear?

rest API:
http://api.backendless.com/...APPLICATION_ID.../...REST_API_KEY.../data/users/...user_object_id(parent_id).../...relationColumnName

Headers:
Content-Type: application/json
user-token: …USER_TOKEN…

Hi morteza hosseini

You used URL like in page Backendless REST API Documentation https://backendless.com/docs/rest/data_explicit_relation_list.html - ?
Method POST - Set relation, method PUT - add relation.
You used method POST or PUT method?

Regards, Vladimir