Here is some general informations about the Iran visa (e0visa) and how to get it :
Visitors to Iran must obtain a visa from one of the Iranian diplomatic missions unless they come from one of the visa exempt countries or countries eligible for visa on arrival.
All visitors must hold a passport valid for at least 6 months.
Tourist visa to Iran is getting easier and easier and Iran is making a lot of progress, hoping to host 20 million visitors in 2025 with easy visa procedures. Visa on arrival is possible for many citizens, for a duration of 30 days, while more countries are getting the visa-free treatment.
Now these are the ways to obtain e-visa to enter Iran :
It is also possible to extend your visa, no matter if you get it at the airport or prior to your arrival. The process is relatively simple, even though the possibility of getting your demand of extension deny still exists.
The Visa On Arrival is not available for the citizens of the following nationalities :
Here's a map of the visa policy of Iran provided by Wikipedia :