Yes, there is a support channel for exactly this, and the response you get depends on the plan you are on, so it is worth knowing the details before anything goes wrong rather than after. Support is normally raised through a ticket from your own admin panel, which is the quickest route because it tells us straight away which portal is affected and what you were doing when the problem appeared. Most plans also include a direct channel for urgent matters where the site is completely unreachable or bookings are failing for every customer.
How fast it gets fixed depends a lot on what has actually broken. If the problem is on our side, something in the portal itself or in the way it is set up, that is ours to fix and we will work it until the site is back. If the problem is a supplier whose system is down or has stopped responding, we can often switch your search over to another supplier you are connected to, but we cannot force a supplier to come back online, and we will tell you plainly when that is the situation rather than leaving you guessing.
There is a difference between a full outage and a smaller fault, and the two are treated differently. A site that is entirely down is picked up as a priority. Something like one search option behaving oddly, or a voucher not formatting the way you want, goes into the normal queue and is worked in turn. Turnaround times and whether you have cover outside ordinary office hours are set by your plan, so a busier agency selling late into the evening should check that it has the right level of cover.
Before you sign off on your plan, ask what the response times are, whether weekend and evening cover is included, and make sure at least two people in your office know how to raise a ticket so you are not stuck if one of them is away.