Please see app2 attached. I changed two lines. You did not have a uitextarea component called "EnterthenragainTextArea" but rather "TextArea". Secondly, There was no subfield "Text", but rather "Value".
app.EnterthenragainTextArea.Text='Choose a valid input';
to
app.TextArea.Value='Choose a valid input';
and
app.EnterthenragainTextArea.Text='Input accepted!';
to
app.TextArea.Value='Input accepted!';
