SSRS Subscriptions cannot be created because the credentials used to run the report are not stored, or if a linked report, the link is no longer valid.
In SSRS subscription, it is requires a Login to connect to the datasource to process the report when subscription will be occurring at its scheduled time.
Please refer to the steps below to solve the issue:
1. In report manager, click the arrow after the report, select Manage.
2. Click Data Sources in the left pane.
3. Select “A custom data source” option. And click option Credentials stored securely in the report server and provide credential information.
4. Then, select Use a Windows credentials when connecting to the data source.
5. Click on apply button.
We also can use the shared data source which is having credential saved into report server.