Customs Charges Products bought online and made in the UK, from the UK

Everything coming from outside the EU is subject to customs duty (once the value including delivery is over €150) and VAT (irrespective of value, very limited exceptions). I'm guessing the value of the bike is well in excess of the duty exemption.

Incorrect.

There are many countries that the EU has agreement for duty exemption.

And there are also many goods that have duty exemption.

Goods manufactured in the UK and the manufacturing process adding substantial value would see no duty being due.

But taric code and country of origin must be declared and be presented to customs for the exemption to be validated.

I suggest you read up on the EU / UK free trade agreement.

Hint in the word "free"

But I'm guessing that as in another thread you do not understand what you are talking about and "guessing" again.

Certainly if goods come from the UK and are made in a third party country - eg a TV made in China, it is liable for duty as the country of origin is China

But if goods are made in the UK and the production process adds significant value, the country of Origin is UK and no customs duty applies (exclusions of alcohol, tobacco and fuel)

Here's the revenue link.

https://www.revenue.ie/en/customs-traders-and-agents/brexit/information-for-businesses/implications-eu-uk-trade-agreement/origin-of-goods-and-tariffs.aspx

The important phrase / statement is that "Country of Origin is UK"

Unless that is clear on the documentation they will assume its made in China

Its a simple key stroke for the courier to change on the import system

That would be the official wording. But simply "UK Origin" is sufficient.

The funny thing is that I can import directly from Japan with 0% duty, but if I purchase the same goods from a UK distributer I pay duty on it