Stored Procedure working correctly in DB MySql but get error in ASP NET C#

I have the Stored Procedure in database MySql version 8.0.17 that working correctly on the DB

CALL SP_PIVOT('Q100', 'sourcetable', 'contents', 'sun', 'contents');

Now I am trying to get Stored Procedure to work in code-behind ASP NET C#

All tests get an error

First test

string sql = "CALL SP_PIVOT('Q100', 'sourcetable', 'contents', 'sun', 'contents');";

MySqlCommand cmd =
    new MySqlCommand(sql);

Error

You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'Q100', 'sourcetable', 'contents', 'sun', 'contents')'' at line 1

Second test

MySqlCommand cmd =
    new MySqlCommand("SP_PIVOT");

cmd.CommandType = CommandType.StoredProcedure;
cmd.Connection = con;
cmd.Parameters.AddWithValue("tun", Mp2smal.Base64ForUrlDecode(Request.QueryString["un"]));
cmd.Parameters.AddWithValue("sourcetable", "sourcetable");
cmd.Parameters.AddWithValue("contents", "contents");
cmd.Parameters.AddWithValue("sun", "sun");
cmd.Parameters.AddWithValue("contents", "contents");

Error

"contents" Parameter is already declared