The first thing you need to do when troubleshooting an integration error is to understand what integration it is. This will help you know where to look for the issue. Were you making a direct ajax call to something? Were you loading a subform? Were you loading/working with a bridge? Are you working with a webhook?
The application log is available under Space -> Logs and is the first stop if you are having any issue where you aren't sure of the cause. This will likely have some kind of error logged. Note that there are multiple log levels available for this log, so
The application log is in the following format
[timestamp] [log level] [thread] [message]
2018-11-07 23:15:08,515 DEBUG [pool-1-thread-2 ] - Processing the Signature Authentication Strategy.
2018-11-07 23:15:08,515 DEBUG [pool-1-thread-2 ] - Adding the body content to the webhook request.
The exception to this format is when an error occurs. It is followed by a stack trace, and those lines don't have all the same format. They are considered part of the previous message/line.
2018-11-07 23:15:08,650 ERROR [pool-1-thread-2 ] - Unable to log completion information about webhook job "f7ef9524-e2e2-11e8-a45f-797b483313dd".
java.lang.RuntimeException: Unexpected parent type: Datastore Submission
The bridgehub logs contain all of the logs for the bridge connections through bridgehub. This log follows the same format as the application log. It will have all of the actual API calls made by the bridge with the parameters listed. This is a good place to check if things seem to be working but you are unsure the parameters getting passed are correct (because the results don't look right). This will also show any connection errors and a count of found records for queries.
In every part of the platform where there are webhooks, there is also a "Jobs" section. This is where the executed instances of the webhooks and any of the their errors live.
Clicking on the Summary of a job will bring up it's details:
Part of the details is the server response, which should contain any detail about the failure. If there isn't enough detail there to figure out the issue, you can check the log on the receiving system.