JSON files aren't shown in Open File Dialog while in the filter

I've created an OpenFileDialog in C# and set its filter to this snippet:

OpenFileDialog openDailog = _MainForm.openFileDialog1; openDailog.Filter = "Json files (*.json) | *.json |Text files (*.txt)|*.txt";

The problem is that it doesn't show JSON files but text files are shown in the windows. Is this filter wrong for JSON files or something else?