BRI wouldn't even take USD cash for us, had to open a dollar account just for that, pay in the cash and then send it from that account. Too much hassle. BNI seemed ok with USD cash as the only option. Mandiri didn't care if you have an account with them or not nor wether you pay in USD or Rupiah. Were definitely the easiest.Good to hear that your wife had an easy experience with Mandiri, but this is likely the exception rather than the rule. The most likely way to succeed in actually paying the USD portion is to bring it in USD cash and in the exact amount.
The last time I attempted to pay this fee, I had $200 in two $100 bills. The BRI cashier didn't have $50 in change, so wouldn't process it. Couldn't pay it in rupiah, couldn't get the change in rupiah, hell, wouldn't even take it after I said to keep the change.
Nor sure wether processes have changed over the last couple of year from other peoples experiences or if it's a bit of pot luck which actual branch in the country you walk into. If you try all 3 banks and have USD and local currency you should deffo be ok though. Rules aren't too strict but processes are never easy in Indonesia... plus minus lol.