elastic-apm-node not register span after express responde

I need to send span to elastic-apm after sending express response.

In my code example, i use setInterval. First express response, after 1 second, i try use startspan, but i got error: Cannot read property 'end' of null

const apm = require('elastic-apm-node').start();  
const app = require('express')(); app.get('/', (req, res) => {  
    setTimeout(() => {  
        span = apm.startSpan("My span");  
        span.end();  
    }, 100)  
    res.json({"teste": "TESTE"});
});

My elastic stack version is 7.6.2