Hi @Bikram Pal,
Thank you for posting in this community.
Please follow the steps below to troubleshoot the issue:
1.Try using the workflow in a subsite in this site collection to see if it works. If possible, run the following command to reactivate the WorkflowServiceStore feature.
Disable-SPFeature -Identity WorkflowServiceStore –Url https://sharepoint.com -Confirm:$false
Enable-SPFeature -Identity WorkflowServiceStore –Url https://sharepoint.com
2.Restart the Service Bus Gateway and the Service Bus Message Broker services in gateway app.
3.Restart User Profile Service and User Profile Synchronization Service from SharePoint's Central Administration.
4.Validate that the user profile synchronization was still working.
5.Restart Workflow Manager Website in IIS.
6.Restart Workflow Manager backend service in the Services console.
7.Restart the server.
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