Freelance writing and tax query.

I’m British, with an ARC/marriage visa and medical insurance, married to a Taiwanese national. I recently completed some writing work for a Taiwanese company (my first work for any Taiwanese business), who now say they need to deduct both 10% tax and 1.91% health insurance before paying me for a one-off job. They also add that they require a government tax ID number or Government Uniform Invoice number.

It’s the first time I’ve done freelance work for any Taiwanese company. I’m a little surprised, since I’d assumed the onus would be on me to pay any tax. But my wife, who also freelances, can file for me at the end of the tax year and, so far as I understand, get it back. But the health insurance thing throws me: I already pay health insurance.

I had a look through Forumosa. Just to clarify, from what I’ve read here I need to:

1 - tell them the work is ‘gao fei/category 9B’ freelance work.

2 - that I already pay my own health insurance (through my wife as a dependant - I’d like to clarify whether or not this is right before writing back to them).

3 - do I need a government tax number? I don’t have one, unless I can use my wife’s.

Any help or suggestions are hugely appreciated, as well as whether I’ve missed anything.