I believe you can claim a maximum of NT$10k a month for rent (as long as your landlord agrees to let you claim on it - many won’t to avoid paying tax themselves on that rental income).
Also, if your taxable income is NT$431,000 then you’re in the 13% band (which runs from NT$370,001 to NT$990,000).
13% of 431k is NT$56,030 - NT$25,900 (progressive tax calculation) = NT$30,130
So you weren’t far out. Claiming on your rent will make a difference - if your landlord says no, you’ll have to claim the standard exemption (44k) - if this is the case you’d be looking at a theoretical tax liability of NT$40,010. Still, you should be getting a nice sum back from the taxman - mine’s a Guinness, thanks.