Li Lian NG

I am running an online fashion website and also selling via Etsy. I have a sale which is valued above 135pounds. In this instance etsy, the marketplace wont be collecting VAT on my behalf. The invoice indeed didnt show any VAT collected. How can I now send the dress over to my buyer in UK (Glasgow) without any hiccups? I have been reading so much and I thought I should register for a HMRC acc. I clicked on the setup link and brought to this page where i have to enter my name, but the National Security Number and UK postal code got me really puzzled. How can we as overseas sellers set up any account in this case?? I also have my own website and thought maybe I should also set up since I might sell some from my own website than via a marketplace. The HMRC is really like something for UK residents / citizens to use for their tax related issues but it wont apply to me residing in Singapore and just selling occasionally to someone in UK. Can someone help!!