I want to contribute for the above answer for some:
Actually, there are many websites that offer Vietnam visa services like https://www.vietnam-visa.com/, https://vietnamvisa.govt.vn, https://www.vietnam-evisa.org/, and many more.
They are all approved by the Vietnam government to process visa service. However, it's worth noting that the one with "govt.vn" is not of Vietnam's government. It is just .govt, not .gov. Many people are often confused by this website, so be careful if you are also.
In fact, they are just service providers working under the visa service. About reliability, it can be said that they are relatively reliable, but the quality of service of each provider will be varied.
Normally, if you don't mind to go to Vietnam embassy / consulate in your local, then you can choose to apply for Vietnam visa at the embassy, but if you are not familiar with the procedures of applying and getting visa, you can consider using these providers. They will work to help you fasten and simplify the process of getting visa. It also does not cost much when you use visa on arrival or e-visa (even cheaper in some cases).