I thought that this example in the docs would solve my issue but it's not quite what I need...

https://formidableforms.com/knowledgebase/frm_after_create_entry/#kb-create-entry-in-form-with-repeating-section

Form A has a repeating section with a field that stores the id of the entry in Form B that has another repeating field that needs an entry added to it based on the values in Form A.

I've used the frm_after_create_entry hook to capture the fields I need in Form A to create the entry in the repeating field in Form B but I can't seem to figure out how to insert the new entry. 

What function do I need to use and how do I need to format the input so it inserts the row in the repeating field properly?

I've tried 

FrmEntryMeta::add_entry_meta( $reg_entry_id, $repeater_field_id, null, $repeating_values );

and

FrmEntryMeta::update_entry_meta( $reg_entry_id, $repeater_field_id, null, $repeating_values );

but neither seem to work. The repeating values is an array with the field id/value pairs and I've tried several different formats but nonthing seems to work. Any help would be much appreciated.