Hi
Peter,
We
suspect that you have not registered your license key before initialization of
syncfusion control in the project. Syncfusion license keys are version and
platform-specific and the generated license key is just a string that
needs to be registered before any Syncfusion control is initiated.
To know
about registering the license key,
https://help.syncfusion.com/wpf/licensing/how-to-register-in-an-application

Note: If you are using any template
file for generating the PDF document, please ensure that the original template
file doesn’t has any license trial warning.
Find the below knowledge base article to know about which version
license key should use in the application,
https://www.syncfusion.com/kb/8951/which-version-syncfusion-license-key-should-i-use-in-my-application
Sometimes, old Syncfusion packages
might be referred from NuGet cache in the project
So, could you please try cleaning your project, clear the NuGet cache
from both “%userprofile%” folder and NuGet installed location, deleting
the bin\obj folders and rebuild your
application, then check whether it resolves the issue?
If you are facing any licensing warning even after registering the
proper license key, refer to the below links to resolve the license warning
message.
https://www.syncfusion.com/kb/12756/how-to-resolve-syncfusion-license-popup-message-or-trial-message-warning
If still not resolved, please
share us the following details to investigate issue from our side,
- List of Syncfusion NuGet packages\assemblies used and its
version,
- Target Framework and Platform of your
application,
- License key registered place,
- License key that you are using.
- Screenshot of the Issue.
Regards,
Prashanth S.