How to use the elastic-apm-node.setCustomContext function in elastic-apm-node

const taskConfigs = await getAllStelaceTasks()

    const filteredTaskConfigs = filterTasks(taskConfigs, refDate, nbMinutes)

    fetchEventsTransaction.end()
    fetchEventsTransaction = null // set null to prevent stopping a second time in the finally block

    for (let i = 0; i < filteredTaskConfigs.length; i++) {
      const taskConfig = filteredTaskConfigs[i]
      const { platformId, env, task } = taskConfig

      const emitEventTransaction = apm.startTransaction('Emit task event via cron')
      apm.setUserContext({ id: platformId })
      apm.addLabels({ env, platformId, eventType: task.eventType })
      apm.setCustomContext({ taskId: task.id })

      try {
        // use redlock to ensure the cron process is handled only by one server at a time
        // even within a distributed system
        const lockResource = `locks:stelace_tasks:${task.id}_${refDate}`
        const lock = await redlock.lock(lockResource, lockTtl)

        const alreadyExecuted = await didStelaceTaskExecute({ taskId: task.id, executionDate: refDate })

        if (!alreadyExecuted) {
          await addStelaceTaskExecutionDate({ taskId: task.id, executionDate: refDate })
          await emitTaskEvent({ platformId, env, task })
        }

        await lock.unlock()
      } catch (err) {

} catch (err) {
      // Sending error when response is sent
      ctx.res.on('finish', () => {
        apm.captureError(err);

        debug('Sent error to APM server');
      });
      throw err;
    } finally {
      // Set custom context data
      const reqId = ctx.state.reqId
        || ctx.reqId
        || ctx.req.id
        || ctx.get('X-Request-Id');
      const custom = { reqId };
      apm.setCustomContext(custom);

      // Set user context data
      apm.setUserContext(
        serializeUser(ctx.state.user)
      );
    }
  };
};