Algol Plus Ltd

You must define javascript function wpo_get_address_autocomplete_init

Sample  code  , you must replace YOUR_API_KEY with your key

add_filter('wpo_custom_init_autocomplete_js_function', function () {
  return 'wpo_get_address_autocomplete_init';
});

add_filter('wpo_custom_init_autocomplete_placeholder', function () {
  return 'Search by Postcode';
});

add_action('wpo_before_render_html_app', function () {

?>

<style><span class="fr-marker" data-id="0" data-type="false" style="display: none; line-height: 0;"></span><span class="fr-marker" data-id="0" data-type="true" style="display: none; line-height: 0;"></span>

    .wpo-custom-autocomplete-list {
    position: absolute;
    background-color: white;
    width: 96%;
    padding: 10px;
    z-index: 100;
    max-height: 200px;
    overflow-y: scroll;
    }

    .wpo-custom-autocomplete-list li {
    cursor: pointer;
    }


    </style>

    <script src="https://getaddress.io/js/jquery.getAddress-2.0.8.min.js"></script>

    <!-- Add after your form -->
    <script>

    function wpo_get_address_autocomplete_init(elem, selectedCallback) {

        var on_select = function (v) {

        selectedCallback({
            address_1: v.line_1,
            address_2: v.line_2 || v.line_3 || v.line_4 || v.locality,
            city: v.town_or_city,
            country: "GB",
            lat: v.latitude,
            lng: v.longitude,
            postcode: v.postcode,
            state: v.county,
            street_number: v.building_number,
        });

        jQuery(elem).val('').trigger('input');
        }

        jQuery(elem).on('input', function () {

        if (!jQuery(this).val()) {
            jQuery(elem).siblings('.wpo-custom-autocomplete-list').remove();
            return;
        }

        jQuery.get(
            'https://api.getaddress.io/find/' + jQuery(this).val(),
            {
            'api-key': 'YOUR_API_KEY',
            expand: true,
            },
            function (d) {

            var ul = jQuery('<ul class="wpo-custom-autocomplete-list"></ul>');

            d.addresses.forEach(function (v, i) {
                ul.append(jQuery('<li data-index="'+ i +'">'+ (v.formatted_address.filter(function () { return !!v; }).join(' ')) +'</li>').on('click', function () {
                    on_select(
                    Object.assign({}, v, {
                        latitude: d.latitude,
                        longitude: d.longitude,
                        postcode: d.postcode,
                    })
                    );
                })
                );
            });

            jQuery(elem).siblings('.wpo-custom-autocomplete-list').remove();
            jQuery(elem).after(ul);

        }, 'json');
        });
    }
    </script>

<?php
});