Oman is changing up how they issue visas. Oman has been transitioning to an eVisa system, allowing visitors to apply online rather than having to go to a consulate. But you could always just get a visa on arrival which was much easier. This change applies to everyone irrespective of what passport you have.
As of March 21, 2018, Oman will only issue tourist eVisas. That means the only way to get a tourist visa to Oman will be online, and not at a consulate or on arrival in Oman.
— eVisa Oman (@OmanEvisa) February 18, 2018
Also of note is that Oman has increased its visa fees, nearly quadrupling it! The cost of tourist visas has increased from OMR5 (13USD) last April to OMR20 (52USD) now.