TS reduces CS outstanding, hence it reduces your Equity. You are repurchasing your shares. So it makes sense to debit it.
The Par value method is being used in this question.
Everytime your repurchase price is less than your issue price, you debit APIC-TS.
Dr T/S (# of shares * Par value)
Dr APIC- CS (difference between par value and issue price times # of shares repurchased)
Cr Cash
Cr APIC-TS (Difference between repurchase price and Issue price times the number of shares repurchased)
Remember, if the repurchase price is greater than issue price, debit RE for difference between repurchase and issue instead of crediting APIC-TS.