Exception and Erorr in my application

SqlConnection con = new SqlConnection("Data Source=MOSTAFA;Initial Catalog=mohasba;Integrated Security=True");

SqlCommand com = new SqlCommand("insert into Ezn_Qaid (Qaid_no,Qaid_date,Maden,Dayn,El_Qema,Qaid_Type,Bayan_Oll) values('" + B_No.Text + "','" + B_Date.Text + "','" + B_m.Text + "','" + B_D.Text + "','" + B_Q.Text + "','" + comboBox3.SelectedIndex + "','" +comboBox1.SelectedIndex+ "')", con);
            
con.Open();
com.ExecuteNonQuery();

The INSERT statement conflicted with the FOREIGN KEY constraint "FK__Ezn_Qaid__Bayan___44FF419A". The conflict occurred in database "mohasba", table "dbo.Bayan", column 'byan_name'.
The statement has been terminated.

create table Ezn_Qaid 
( 
Qaid_no nvarchar(20) , 
Qaid_date nvarchar(10)  , 
Maden float , 
Dayn float, 
El_Qema float,
Qaid_Type nvarchar(15) , 
--byan_name int NOT NULL,   -- this is the new column 
Bayan_Oll nvarchar(100) FOREIGN KEY (Bayan_Oll) REFERENCES Bayan(byan_name ),
Bayan_Bank nvarchar(100) FOREIGN KEY (Bayan_Bank ) REFERENCES Bank(byan_name ),
Bayan_3momya nvarchar(100) FOREIGN KEY (Bayan_3momya) REFERENCES msaref_3momya(byan_name ),
Bayan_Tkalef nvarchar(100) FOREIGN KEY (Bayan_Tkalef) REFERENCES tkalef_nshat (byan_name )
) 

create table Bayan
(
byan_no int identity ,
byan_name nvarchar(100)PRIMARY KEY
)