Need help pls ,,Building a Bike Rental Shop

Tell us what’s happening:
Describe your issue in detail here.

Your code so far

echo -e "\n~~~~~ Bike Rental Shop ~~~~~\n"

MAIN_MENU() {
  if [[ $1 ]]
  then
    echo -e "\n$1"
  fi

  echo "How may I help you?" 
  echo -e "\n1. Rent a bike\n2. Return a bike\n3. Exit"
  read MAIN_MENU_SELECTION

  case $MAIN_MENU_SELECTION in
    1) RENT_MENU ;;
    2) RETURN_MENU ;;
    3) EXIT ;;
    *) MAIN_MENU "Please enter a valid option." ;;
  esac
}

RENT_MENU() {
  # get available bikes
  AVAILABLE_BIKES=$($PSQL "SELECT bike_id, type, size FROM bikes WHERE available = true ORDER BY bike_id")

  # if no bikes available
  if [[ -z $AVAILABLE_BIKES ]]
  then
    # send to main menu
    MAIN_MENU "Sorry, we don't have any bikes available right now."
  else
    # display available bikes
    echo -e "\nHere are the bikes we have available:"
    echo "$AVAILABLE_BIKES" | while read BIKE_ID BAR TYPE BAR SIZE
    do
      echo "$BIKE_ID) $SIZE\" $TYPE Bike"
    done

    # ask for bike to rent
    echo -e "\nWhich one would you like to rent?"
    read BIKE_ID_TO_RENT

    # if input is not a number
    if [[ ! $BIKE_ID_TO_RENT =~ ^[0-9]+$ ]]
    then
      # send to main menu
      MAIN_MENU "That is not a valid bike number."
    else
      # get bike availability
      BIKE_AVAILABILITY=$($PSQL "SELECT available FROM bikes WHERE bike_id = $BIKE_ID_TO_RENT AND available = true")

      # if not available
      if [[ -z $BIKE_AVAILABILITY ]]
      then
        # send to main menu
        MAIN_MENU "That bike is not available."
      else
        # get customer info
        echo -e "\nWhat's your phone number?"
        read PHONE_NUMBER

        CUSTOMER_NAME=$($PSQL "SELECT name FROM customers WHERE phone = '$PHONE_NUMBER'")

        # if customer doesn't exist
        if [[ -z $CUSTOMER_NAME ]]
        then
          # get new customer name
          echo -e "\nWhat's your name?"
          read CUSTOMER_NAME

          # insert new customer
          INSERT_CUSTOMER_RESULT=$($PSQL "INSERT INTO customers(name, phone) VALUES('$CUSTOMER_NAME', '$PHONE_NUMBER')") 
        fi

        # get customer_id
        CUSTOMER_ID=$($PSQL "SELECT customer_id FROM customers WHERE phone='$PHONE_NUMBER'")

        # insert bike rental
        INSERT_RENTAL_RESULT=$($PSQL "INSERT INTO rentals(customer_id, bike_id) VALUES($CUSTOMER_ID, $BIKE_ID_TO_RENT)")

        # set bike availability to false
        SET_TO_FALSE_RESULT=$($PSQL "UPDATE bikes SET available = false WHERE bike_id = $BIKE_ID_TO_RENT")

        # get bike info
        BIKE_INFO=$($PSQL "SELECT size, type FROM bikes WHERE bike_id = $BIKE_ID_TO_RENT")
        BIKE_INFO_FORMATTED=$(echo $BIKE_INFO | sed 's/ |/"/')
        
        # send to main menu
        MAIN_MENU "I have put you down for the $BIKE_INFO_FORMATTED Bike, $CUSTOMER_NAME."
      fi
    fi
  fi
}

RETURN_MENU() {
  echo "Return Menu"
}

EXIT() {
  echo -e "\nThank you for stopping in.\n"
}

MAIN_MENU

Your browser information:

User Agent is: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_7) AppleWebKit/605.1.15 (KHTML, like Gecko) Version/15.5 Safari/605.1.15

Challenge: Build a Bike Rental Shop

Link to the challenge:

I’ve edited your post for readability. When you enter a code block into a forum post, please precede it with a separate line of three backticks and follow it with a separate line of three backticks to make it easier to read.

You can also use the “preformatted text” tool in the editor (</>) to add backticks around text.

See this post to find the backtick on your keyboard.
Note: Backticks (`) are not single quotes (').