I paid it via direct deposit from my bank to the account number given by ROP. I sent them the proof of payment via courier.
As an additional thing, did you have to get it attested by the Ministry of Foreign Affairs? Alternatively, does the certificate mention this at the bottom (as it does on the one I received)?
For anyone else following this thread, here's what worked for me:
1. I live in Canada so I emailed
dgfacid@rop.gov.om explaining my situation.
2. They requested I send them documents via PDF file format (no fingerprints since I already had an Omani Resident card from back in the day).
3. They mentioned nothing about any specific background for the photo so I just sent in what I had (white background).
3. Went to a TD branch and wire transferred the fee and sent them the proof via email (PDF) as they asked.
4. Got a PDF copy in 5 days and a physical one mailed to me in 10.
The difficulty it seems with this is the fact that the entire process is pretty disorganized with incomplete information or no information available on the internet. I hope this helps someone.