In general, travel expenses are only reimbursed to employees if the travel is on behalf of the company (e.g. if the company asks you to travel from Zagreb to Vienna to meet a client or similar).
If you decide on your own to travel to another city or country (regardless of being on-site with the client, working in a 9Y office or by the sea) to work, you have to take care of the organisation of your travel yourself and pay your own costs. You might be able to use your Personal Budget to cover these costs.
On the subject of client meetings etc: If the client wishes you to be present at his place, it must be clarified with the client before booking the trip that these costs can also be invoiced to them to the actual extent (plus a small expense allowance if necessary). It should not happen that the client is not aware of this and that we have to bear the costs ourselves in the end.