facing the exact same problem.
but cant use your update_post_meta solution because its a repeater in a repeater where i have to add a new row.
i looked up in the database but the meta_key from the second repeater is = subrepeater_ and not repeaterName_0_subrepeater_0_subsubfield.
so how can i refer to the right row in the repeater and add a field in the subrepeater?
