Citizens from all European countries need a visa for stays up to 30 days. The passport should be valid for at least six months at the time of entry. The visa is available for short trips up to 30 days via the online application (ETA) for entries. Usually, you will receive the visa within 24 hours by e-mail to the e-mail address you provided. 

The payment of the fee is possible only by credit card. Copies of the flight booking and itinerary in Sri Lanka with hotel addresses are also required. Basically, it is an online visa. If necessary, it can also be applied at the airport in Colombo, but then it will cost about 20% more.

Further information as well as the fees can be found on the official website of the Department of Immigration & Emigration in Sri Lanka.