SEPA payments are not free between different banks in all countries. There can be charges of 4€ within the same country, even for small amounts.
Interestingly, Erste have it off by default in the mobile app so I always have to turn it on for each transfer.
Non-free transfers between those banks can take about 1 hour but if too late in the day then 1 business day.
SEPA instant might cost extra or not be available but both of that will change soon due to new EU regulations.