In general the below error usually occurs when the server is running and tries to retrieve the license, but there is no response, then it will enter the grace period.If a Denodo server stops working unexpectedly, you have to manually notify the License Manager that the license that this Denodo server was using, is no longer in use. Otherwise, the license will be considered in use until the grace period expires (5 days since the last time this Denodo server renewed its license).
> 902819910 [main] ERROR 2023-05-22T12:28:40.548 com.denodo.solutionmanager.Info  - Error sending license ACK. Server starts to use a grace period of 7200 minutes. Grace period finishes at Sat May 27 12:28:40 EDT 2023
Hence to freeup license usage, I would perform the following:
1.Send a request to the following endpoint by replacing the appropriate values for <Port> and <Host> of License Manager and VDP servers:
2.Restart the Virtual DataPort server.
For more information you could refer to the Free license Usage section of [**REST** **API**](https://community.denodo.com/docs/html/browse/latest/en/solution_manager/administration/appendix/rest_api/rest_api#free-license-usage) User Manual.
If you still need help and if you are a user with valid support access then you can raise a support case in Denodo Support Site so that our support team can help you.
Hope this helps.