Originally Posted by
konoyaro
It would be disappointing if Amex is interpreting tax payments as "fees or interest charges".
Those are only two of the excluded categories:
Eligible purchases do NOT include fees or interest charges, balance transfers, cash advances, purchases of travelers checks, purchases or reloading of prepaid cards, or purchases of other cash equivalents
...but tax payments are not excluded. The agent is simply making up an explanation because s/he does not know why the points have not posted.