Can't select multiple contacts-One to many relate field

I have made one-to-many relationship between two modules Ads and Contacts…Made a custom relate field in Ads and placed it in edit view which opens sub panel of contacts.The reason is when creating an Ads user can select multiple contacts.But the issue is I can only select one contact from Ads create screen.How can i achieve this?or is their any other way to do this please guide i have searched a lot to do this but couldn’t find anyway.

Current result:


I need it like this:

I have the same question
how can i select multiple contacts in a relationship one-to-many field?