Hi ambikaTewari__ATCI
From your description, the first step could be to ensure that the uniqueEventId is properly generated and captured. This can be done for example by sending the ID in context data to verify or logging it to debug logs. if this is for the web, use the browser’s developer console to log the uniqueEventId. For instance, for web you can use _satellite.logger.info to log the value. For mobile apps, this could be by logging the event ID to the app logs depending on the specific mobile platform’s logging method.
Value length shouldn't be an issue, as the values get truncated to 20 characters. And as values are hexadecimals, they also should be alphanumeric, which is accepted.
Hope this helps!