Covering offer quest HELP

Go to your stallion’s page and under the breeding section, there’s a button called “cover a mare.” Click that, select either public or reserved for one of your mares, and then choose a price. Click confirm.

If you choose one of your own mares, you have to select a mare and then confirm.

I think for this objective just making the offer is enough. You don't have to accept it with a mare.
So just go to the stallion's page, click the 'Cover a mare' button and set the price.

To explain further: If you breed horses, you can do that by clicking the 'Cover my mare' button and choose a stallion.
But that is not *offering* a cover, that is *taking* one.
For this, you need to take one of your *own* stallions, on his page click the 'Cover a mare' button and offer the covering to either one of yours, to a specified mare of any other player or to the public.

Of course if you chose for one of your own mares, you can go to her page and accept the covering offer, but that is not needed for this objective. The objective is only about the *offer*.