Brussels to Bruge

At the window you can pay cash and with credit card. Cash is never a problem. You can buy them the day before to avoid a possible queue when you want to get your train.
By the way: I don't understand your question about payment in dollars. Dollars are no official currency in Europe. (They have been invented here under the name of talers, but that was ages ago.)

The machines don't take chip credit cards. You have to wait in line for a human, who does take chip cards. Trains are frequent, unreserved, and crowded. Ask your card company if they charge 3% for Foreign Transaction. For more info, see our host's website, top left.

We bought tickets at machines with credit/debit cards there were also windows to pay cash/credit.

I bought mine at the station before I got on the train (about 8 am), got it at the ticket window, paid cash (€). No problem, no line, and that was in July - peak tourist season.

i'm pretty sure you can buy it online and print it out.
and it is valid on that route for the day (meaning you do not have to get on at a set scheduled time)

Keith, thank you for your update; I haven't been to Belgium in two years. Did you really buy local train tickets at a wall-side vending machine using an American chip card? That would be huge change in Belgian railway policy, and very helpful to daytrippers. Did you get any feeling about whether there was (for example) a maximum transaction cost because you have (?) a Chip-and-Signature card?