You need to add Interrail/Eurail Global Pass discount, then select one-way tickets and it should give you prices of 0€. You click on it and then add a 3€ reservation.

Btw it is optional but you can do it for peace of mind

Let me know if it doesn't work

"Seat reservation only” should work for these trains. Maybe there are engineering works and timetables are not final yet. It's very unusual not to be able to book any seats 4 weeks in advance. 21 and 24 April work fine so I think reservation is just not open yet.

Thanks. I have applied the Interrail discount but for travel over this weekend this makes no difference to the offer of “Ticket not available”. I have discovered that there is DB Netz construction work affecting this route over that weekend but it seems strange that I can buy a ticket but not make a reservation only. There is another option of travel by WESTBahn trains, although there are only three on the Sunday. By WESTBahn it is a clear rail replacement bus between Salzburg and Innsbruck but note that this requires a mandatory - FREE - reservation via westbahn.at.

If the train line is closed, the RJX trains to/from Zürich (every 2 hours) will run via Zell am See. All others will be normaly replaced by busses between Kufstein and Salzburg.

I’m facing the same issue :(

I thought it could be related to seat availability or something similar, but I found more crowded days with availability for seat reservation only on the search, so I’m not sure why it is unavailable at the moment.

I’ve sent an e-mail to the customer support asking for details, and I’ll share the response once I hear back from them.

Update for anyone else making this journey over the weekend 22/23 April. It is now possible to make a reservation only booking for services provided by OBB. As expected the journey will involve an ‘SV200’ rail replacement bus, at least on the 23rd, between Salzburg Hbf and Wörgl Hbf (Vorplatz) then onward connection either by an EC or Cityjet Xpress. Thanks for earler discussion / advice.