Postgresql. Create function get_ticket - postgresql

Question

Create a function to Get Ticket (for a Reservation).Ticket a booked reservation when the passenger pays the total amount.
Create a trigger, called line disruption, that adjusts all the tickets to the immediate next line when a line is closed due to an accident or maintenance, unless the customer specified no substitutions/adjustments in which case the ticket is canceled.
I created the tables, but I have some mistakes on my function: Please show me the mistakes and explain your solutions.
CREATE OR REPLACE FUNCTION get_ticket (reservation_id int, id int, price int)
RETURNS SETOF ticket
AS $$
BEGIN
INSERT INTO Ticket (ticket_id, reservation_id, price);
END;
$$ LANGUAGE plpgsql;
CREATE TABLE Customer (
id int PRIMARY KEY,
fname varchar,
lname varchar,
street varchar,
town varchar,
postal_code varchar
);
CREATE TABLE Station (
id int PRIMARY KEY,
name varchar,
open_time varchar,
close_time varchar,
stop_delay int,
street varchar,
town varchar,
postal_code varchar
);
CREATE TABLE Train (
id int PRIMARY KEY,
name varchar,
description varchar,
seat_avail int,
top_speed int,
cost_per_km int
);
CREATE TABLE Rail_Line (
line_id int PRIMARY KEY,
speed_limit int
);
CREATE TABLE Passes_Thru_SRL (
line_id int PRIMARY KEY,
station_id int PRIMARY KEY,
distance int,
CONSTRAINT FK1_SRL FOREIGN KEY (line_id) REFERENCES Rail_Line (line_id) ON DELETE CASCADE,
CONSTRAINT FK2_SRL FOREIGN KEY (station_id) REFERENCES Station (id) ON DELETE CASCADE
);
CREATE TABLE Route (
route_id int PRIMARY KEY
);
CREATE TABLE Passes_Thru_SR (
route_id int PRIMARY KEY,
station_id int PRIMARY KEY,
stops bool,
CONSTRAINT FK1_SR FOREIGN KEY (route_id) REFERENCES Route (route_id) ON DELETE CASCADE,
CONSTRAINT FK2_SR FOREIGN KEY (station_id) REFERENCES Station (id) ON DELETE CASCADE
);
CREATE TABLE Route_Schedule (
route_id int PRIMARY KEY,
day varchar,
time varchar,
train_id int PRIMARY KEY,
CONSTRAINT FK1_RS FOREIGN KEY (route_id) REFERENCES Route (route_id) ON DELETE CASCADE,
CONSTRAINT FK2_RS FOREIGN KEY (train_id) REFERENCES Train (id) ON DELETE CASCADE
);
CREATE TABLE Reservation (
reservation_id int PRIMARY KEY,
price int PRIMARY KEY,
id int,
CONSTRAINT FK_RS FOREIGN KEY (id) REFERENCES Customer (id) ON DELETE CASCADE
);
CREATE TABLE Ticket (
ticket_id int PRIMARY KEY,
reservation_id int,
id int, price int,
CONSTRAINT FK_RS1 FOREIGN KEY (reservation_id) REFERENCES Reservation (reservation_id) ON DELETE CASCADE,
CONSTRAINT FK_RS2 FOREIGN KEY (id) REFERENCES Customer (id) ON DELETE CASCADE,
CONSTRAINT FK_RS3 FOREIGN KEY (price) REFERENCES Reservation (price) ON DELETE CASCADE
);