When we collect ("poll") reservations from OTA's, we ask them "Do you have any bookings for any Caterbook users?"
They then respond with any new, modified or cancelled bookings that have been made since the last time we asked and we distribute them to each property. This time period between each polling event is short, typically 1 minute.
Occasionally our request isn't responded to correctly, and so any outstanding reservations would usually be pulled down at the next poll, 1 minute later.
If you see an OTA SYnc In error mentioning "500" error (or 501, 502, 503), this is a response from the OTA telling us that they have got a problem at their end serving our request. This may be due to any number of reasons, but we try again 1 minute later, and again... It doesn't mean your property has necessarily "missed" a booking being imported, this is a global error that every property connected to the affected OTA will see.
In the event that an OTA has a serious outage meaning that reservation delivery via XML is affected, they will usually deliver any reservations by alternative means, typically after 30 minutes via email and these would need to be manually input into Caterbook.
Please see the following related article regarding OTA Sync Out errors.