Hi,
There are lot of details missing in your request but I will try to answer based on assumptions. I would assume you are using diagnostic logs with sending them to Log Analytics workspace. In such case if you are using the new Resource-specific option for sending logs the logs are send to ApiManagementGatewayLogs table. That table supports Ingestion-time transformation feature. In short that feature allows you to change the structure of the received logs or for example to filter out certain logs based on the values of different columns by using KQL (kusto query language) queries. That feature has some additional cost which you will find at Log Processing in Azure Monitor pricing.
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