Eligible for Child Tax Credit but it's not being applied

I am eligible for the child tax credit (x3 children) but it's not being applied, with the reason given that my taxable income is $0.   However, it's also showing that I owe $2500 on my federal return.  I am self-employed and live in the UK, so I receive the Foreign Earned Income Exclusion which is why my taxable income is $0.  But the $2500 comes from the self-employment tax --- my understanding is that the Foreign Earned Income Exclusion does not apply to this.   The Child Tax Credit should though -- at least it did last year.  (Notwithstanding the fact that the UK has a reciprocal agreement with the US for social security?).   How can I fix this please?   Thanks.