setValue of Dropdown

[Memurame]

I have two select fields.
One customer_id contains all customers.
The second one contains all projects of the customer.
Now I always reload the projects when the customer_id is changed.

Now when I load the page and want to select the option in the projects dropdown, unfortunately it doesn't work. The entries are available in the dropdown, but it does not select the corresponding option.

Can someone help me here with my problem?
I hope I could describe my problem so that you understand it.

Here is my JS code:

$(document).ready(function () {

    if($('#project_id').length){
        let tomselectProject = new TomSelect($('#project_id'), {
            valueField: 'id',
            labelField: 'name',
            copyClassesToDropdown: false,
            dropdownParent: 'body',
            controlInput: '<input>',
            load: function (query, callback) {

                var url = rootUrl + '/api/0/customer/' + query + '/projects';

                fetch(url)
                    .then(response => response.json())
                    .then(json => {
                        callback(json);
                    });

            },
            render: {
                item: function (data, escape) {
                    if (data.customProperties) {
                        return '<div><span class="dropdown-item-indicator">' + data.customProperties + '</span>' + escape(data.name) + '</div>';
                    }
                    return '<div>' + escape(data.name) + '</div>';
                },
                option: function (data, escape) {
                    if (data.customProperties) {
                        return '<div><span class="dropdown-item-indicator">' + data.customProperties + '</span>' + escape(data.name) + '</div>';
                    }
                    return '<div>' + escape(data.name) + '</div>';
                },
            }
        })
        $('#customer_id').bind('change', function () {
            var selected = $(this).children("option:selected").val()
            var select = $('#project_id').data('selected')
            console.log(select)
            tomselectProject.clear()
            tomselectProject.clearOptions()
            tomselectProject.load(selected)
            tomselectProject.setValue(select)
        });

        $('#customer_id').trigger('change');
    }

Here the HTML Code

<div class="row mb-3">
                            <div class="col-6">
                                <label for="customer_id" class="form-label">Kunde <span class="text-danger">*</span></label>
                                <select class="form-select tomselect-search" name="customer_id" id="customer_id">
                                    <option value="0">-- Kunde auswählen --</option>
                                    <?php foreach($customers as $customer): ?>
                                    <option value="<?=$customer->id ?>"
                                        <?= ($website->customer_id == $customer->id) ? 'selected' : '' ?>>
                                        <?= $customer->customername ?>
                                    </option>

                                    <?php endforeach; ?>
                                </select>
                            </div>
                            <div class="col-6">
                                <label for="project_id" class="form-label">Projekt</label>
                                <select class="form-select" name="project_id" id="project_id" data-selected="<?=$website->project_id?>">

                                </select>
                            </div>
                        </div>