Please check if the ObjectDataSource component is configured to map the custom method's arguments to report parameters - ObjectDataSource Wizard (step 3)
, and if the types are synchronized - Report Parameters
. Then test running preview in the Report Designer.
If the preview at design-time is successful, and only the preview in viewer fails, test to upgrade Newtosoft.Json.dll
via VS Nuget Packages
The recommended troubleshooting approach is to use Fiddler or other proxy tool to check the requests, their responses and statuses. Information about requests and responses content can be seen in Fiddler - Inspectors - Request/Response - Raw tabs. Thus you can check if report parameters' values are submitted correctly - if the message is constructed correctly.
Let us know if you need any further help.
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