Hi Tommy,
Thank you for contacting Syncfusion Support.
We suggest you to check the “Id” of the component and the “document.getElementById” statement is placed inside the change function, which is mentioned in the change property of the ComboBox component.
If issue persists, kindly send us the screenshot where the error produce and more details along with the code snippet.
Please refer to the sample in the below location,
Regards,
Ilakkiya B