Source code for https://formidable-masterminds.com/use-frmentry-create-with-dynamic-fields

masterminds_get_dynamic_field_entry_id_by_value.php

<?php
/* use this function for populating entries where
 * dynamic lookup entry ids are required
 */
function masterminds_get_dynamic_field_entry_id_by_value( $field_id, $value ) {
    global $wpdb;
    $frm_item_metas_table = $wpdb->prefix . 'frm_item_metas';
    $sql = "SELECT item_id FROM `{$frm_item_metas_table}` WHERE field_id = '{$field_id}' AND meta_value = '{$value}'";
    return $wpdb->get_var($sql);
}

pre_pop_forms.php

<?php
add_action('frm_after_create_entry', 'pre_pop_forms', 30, 2);
function pre_pop_forms($entry_id, $form_id){
    if ( $form_id != 52 ) {
        return;
    }

    /* bullet proof FrmEntryMeta::add_entry_meta() to avoid duplicate entries
     * of the client entry id field on form 52 if the record is edited and you
     * are also using the frm_after_update_entry filter
     * vmf - 10/23/2023
     */

    /* test for current value */
    $current_value = FrmEntryMeta::get_entry_meta_by_field( $entry_id, $field_id );

    /* if no current value, add the field */
    if( is_null( $current_value ) ) {
        /* if successful, function returns entry id of meta data record */
        $added = FrmEntryMeta::add_entry_meta( $entry_id, $field_id, null, $entry_id );
    } else {
        FrmEntryMeta::update_entry_meta( $entry_id, $field_id, null, $entry_id );
    }

    /* add entry to form 2 */

    /* make sure user id is populated */
    if ( !isset( $_POST['frm_user_id'] ) ){
        return;
    }

    /* get form 2 id from key for transportable code
     * see https://formidable-masterminds.com/writing-transportable-code-keys-vs-ids/
     */
    $form2 = FrmForm::get_id_by_key('form2_key');

    /* get field id by keys for transportable code */
    $dynamic_lu_field = FrmField::get_id_by_key('status_lu_field');
    $form2_entry_id_field = FrmField::get_id_by_key('form2_entry_id');
    $form2_status_id_field = FrmField::get_id_by_key('form2_status_id');

    /* get record id for "Pre-pitch" status */
    $status_id = masterminds_get_dynamic_field_entry_id_by_value( $dynamic_lu_field, "Pre-pitch" );

    //create entry
    FrmEntry::create( array(
        'form_id' => $form2,
        'frm_user_id' => $_POST['frm_user_id'],
        'item_meta' => array(
            $form2_entry_id_field => $entry_id,
            $form2_status_id_field => $status_id,
            ),
        )
    );
}