optional parameters must appear after all required parameters in c# [duplicate]

Answer 1

You need to move your optional parameters to the end of the parameter list:

from MSDN:

Optional parameters are defined at the end of the parameter list, after any required parameters. If the caller provides an argument for any one of a succession of optional parameters, it must provide arguments for all preceding optional parameters. Comma-separated gaps in the argument list are not supported. For example, in the following code, instance method ExampleMethod is defined with one required and two optional parameters.

public List<IndentItems> GetIndentFilledInfo(
        List<SurveyFeedback> surveyFeedbacks, 
        bool hasupdate,
        string ddlevent,
        string indentType = null)

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Answer 2

optional params should be after all of you method params:

public List<IndentItems> GetIndentFilledInfo(
    List<SurveyFeedback> surveyFeedbacks, 
    bool hasupdate, 
    string ddlevent,
    string indentType = null)    
{
    // Codes here
}

MSDN