您可以将参数附加到（固定）url。
在客户端javascript中处理sseMessage事件。

document.body.addEventListener('htmx:sseMessage', function (evt) {

        //* check if this event is the one you want to use
        if (evt.detail.type !== "order_complete") {
            return;
        }

        //* If a JSON string was sent, leave it as it is 
        //evt.detail.elt.setAttribute("hx-vals", evt.detail.data);

        //* if not
        var msg = {};
        msg.orderId = evt.detail.data;   
        evt.detail.elt.setAttribute("hx-vals", JSON.stringify(msg));
    });

请参阅https://htmx.org/attributes/hx-vals/
如果evt.detail.data是123：

/orders/showmodal?orderId=123

HTML：

<div hx-ext="sse" sse-connect="/sse-something">
        <div hx-get="/orders/showmodal"
                hx-trigger="sse:order_complete"
                hx-swap="innerHTML"
                hx-target="#idModalPlaceholder">
        </div>
    </div>

更新

您也可以只针对order_complete使用事件侦听程式。

document.body.addEventListener('sse:order_complete', function (evt) {

        //* If a JSON string was sent, leave it as it is 
        //evt.detail.elt.setAttribute("hx-vals", evt.detail.data);

        //* if not
        var msg = {};
        msg.orderId = evt.detail.data;   
        evt.detail.elt.setAttribute("hx-vals", JSON.stringify(msg));
    });