Your hotel need to provide a letter of booking confirmation with SHA+ logo on it. (Sample attached) Confirmation from travel agent like Agoda etc. won’t work. If you book via online travel website then you will need to call hotel to email you SHA+ letter. If your application rejected, you should receive an email within couple hours inform you the reason and asking for you to supple more documents. But if you done it and your ref no. disappeared, just apply again. You can also reach @ThaiConsular via Line app. They are very good at responding all questions regarding Thailand Pass.