Add Custom Fields to the "New Subaccount" Section.

You may want to add custom fields connected to user meta keys, available when a new subaccount is created or edited.

You can use the following snippet:

add_action('b2bking_custom_new_subaccount_fields', function($user_id = 0){

	?>
	<br>
	<div class="b2bking_subaccounts_new_account_container_content_element">
		<div class="b2bking_subaccounts_new_account_container_content_element_label">
			<?php esc_html_e('Store Code','b2bking'); ?>
		</div>
		<input type="text" class="b2bking_subaccounts_new_account_container_content_element_text" name="b2bking_store_code" placeholder="<?php esc_attr_e('Enter the store code here...','b2bking'); ?>" <?php if($user_id !== 0){echo 'value="'.esc_html(get_user_meta($user_id,'storecode', true)).'"';}?>>
	</div>
	<div class="b2bking_subaccounts_new_account_container_content_element b2bking_subaccount_horizontal_line">
		<div class="b2bking_subaccounts_new_account_container_content_element_label">
			<?php esc_html_e('Store ID','b2bking'); ?>
		</div>
		<input type="text" class="b2bking_subaccounts_new_account_container_content_element_text" name="b2bking_store_id" placeholder="<?php esc_attr_e('Enter the store id here...','b2bking'); ?>"  <?php if($user_id !== 0){echo 'value="'.esc_html(get_user_meta($user_id,'storeid', true)).'"';}?>>
	</div>
	<?php
});

add_filter('b2bking_custom_new_subaccount_field_names', function($fields){
	$fields = array('b2bking_store_code', 'b2bking_store_id');
	return $fields;
}, 10, 1);

add_filter('b2bking_custom_field_meta', function($field_name){
	// you can set a custom user meta key here
	if ($field_name === 'b2bking_store_code'){
		$field_name = 'storecode';
	}
	if ($field_name === 'b2bking_store_id'){
		$field_name = 'storeid';
	}
	return $field_name;
}, 10, 1);

Explaining the snippet:

The first action in the snippet adds the HTML for the fields
Then in the filter you must enter the names of the custom field(s)
Finally, this is optional, the last filter ties each name to a specific user meta key

This snippet adds 2 fields there visually: