investment in debt : Transaction cost

Hi Chris

what happens to the transaction cost please under the investment in debt in all 3 cases

1) Amortised

2) FVTOCI

3) Fair value for trading

Additionally i am aware that credit losses are applicable on amortised cost debt and not fair value, because once we recognize the asset at its fair value , the credit impairment will make no sense

but i keep on hearing it is applied on FVTOCI as well, how ? and wouldnt it be rendered meaningless as well

Thanks