Hello Mario,

I am not sure which report designer you have used to preview the report but I will assume that you mean the Standalone Report Designer application since it is the most widely used of the available designers. The Standalone Report Designer is a .NET Framework application. In .NET Framework we do not use the System.Text.Json, thus this limitation is not present and you do not see the error when you preview the same report in the designer application.

If you wish to work around this problem, you can create a reporting rest service in .NET Framework 4.5, for example, and you can use this service with the Blazor report viewer.

The less reliable option is the workaround from the System.ArgumentException The JSON value of length n is too large and not supported KB article but it will not work 100% of the time. What this KB suggests essentially is to disable the search metadata and thus lower the total data so that the report does not exceed the limit but even without the search metadata, the data could still be too much so it depends on the report.

I hope that at least one of the two workarounds will help.

Regards,
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Hello Catalin,

In .NET Core, we use the System.Text.Json serializer which is limited to 125MB of data, thus large reports that exceed that limit will encounter this issue.

For more information, please have a look at The JSON value of length n is too large and not supported #2 #39953 Github thread.

Regards,
Dimitar
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