Much of this (as admitted in the tweet thread) is due to the VAT changes, I don't think it is wise to blame this on Brexit and move on as it ignores the growing problem. The only connection Brexit has to this is timing, these VAT changes are EU wide and will rolled out to EU member states this year. Foreign companies will need to charge VAT at the member states rate (some have multiple) and register for VAT in the EU.

After the EU other countries will follow suit wanting their slice of the pie, if you don't believe me have a look at global sales tax handling for digital sales ([0] quick example). Trying to stay above board here is difficult, there is investment to be made in charging the correct taxes in the first place but the main problem is the massive amount of potential paperwork in filing all the taxes. As will be the case for many retailers we simply don't sell to any country which requires us to charge tax and has no sales threshold.

This is a big problem for small business, in an age where anyone can start a niche business and scrape a customer base together from the entire world they will be killed by paperwork...

[0] https://quaderno.io/blog/digital-taxes-around-world-know-new...