They contact you, not us. A white label portal carries your brand from the first page to the confirmation email, so your travellers will never see any sign that another company is behind the technology. That is the point of white label, and it means you stay the face of the business for every question a customer has, at any hour. We sit behind you and support your team, not your travellers.
It helps to separate two kinds of problems. If the portal itself is misbehaving, for example searches will not load or a payment page will not complete, that is something to raise with us and we will look into it. If the issue is with the booking, for example a hotel says it has no record of the reservation or an airline has moved a flight, that is a supplier matter. We can help you chase it and tell you what the supplier has sent back, but the final answer comes from the airline or the hotel chain, and sometimes that takes longer than anyone would like.
How quickly we respond, and whether cover runs through nights and weekends, depends on the support arrangement in your plan. Urgent faults that stop bookings going through are normally handled differently from general questions, so it is worth knowing in advance which category your problem falls into.
Before you go live, check what support hours your plan includes, and set up your own out of hours arrangement for travellers, even if it is just a mobile number on your confirmation emails and a note telling staff to keep the booking reference handy.