Delphi send null string to webservice

I'm using my WebService from Delphi application, but,开发者_StackOverflow社区 in my webservice, the parameter's value always get null.

Here is my web service code in .net

[WebMethod] int ExecSQL(string ASQL) { }

in delphi I use like this : Delphi Method for using web service which I have used

I don't know what is wrong ? my delphi application or my .net webservice ?

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Add this service unit:

InvRegistry.RegisterInvokeOptions(TypeInfo(xxx), ioDocument);

Read here: https://www.bobswart.nl/weblog/Blog.aspx?RootId=5:798