Sometimes the room price changes between my customer searching and paying, can that be stopped?

No, that cannot be stopped completely, and it is normal behaviour for every hotel booking API rather than a fault in your portal. The results your customer sees on the search page are a snapshot of what the supplier sent back a moment earlier. Hotels and the suppliers who sell them change availability and rates constantly, so by the time your customer has compared options, filled in guest names and reached the payment page, the live rate for that exact room may no longer be the same one they first saw.

What the system can do is check the rate again with the supplier just before payment is taken, so nobody is quietly charged a different amount. If the rate has moved, your customer is shown the current amount and asked to confirm before going ahead, and if the room has sold out in the meantime they are told that too instead of getting a failed booking afterwards. Your markup rules stay applied on top, so the selling logic you have set does not change just because the underlying rate did.

How often this happens honestly depends on the supplier, the destination and how busy the dates are. Some suppliers hold a searched rate for a short period and others make no such commitment, and which suppliers sit behind your account depends on your plan and the connections set up for you. Popular cities in peak season will see more movement than quiet ones.

If it is happening often enough to annoy your customers, note down a few examples with the city and dates and send them to our support team so we can see which supplier the rates came from and whether the search behaviour can be tuned for you.