Error: When Clicking Submit on Qoute page.

[offternet]

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UPDATE 3: New Install of currenct code:
(A.) Create Customer - worked
(B.) Customer not searchable in Quotes Page (typed full name: Bobby)

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UPDATE 2: Changed utf8mb4_0900_ai_ci to utf8mb4_general_ci in quotes_items table and stock-db.sql insertion worked successfully.

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UPDATE 1: RESOLVED by UPDATE 2 above:
Test Database sql insertion of current stock-db.sql resulted in this error:
Error
SQL query: Copy

---

--
-- Table structure for table quote_items

CREATE TABLE quote_items (
id int NOT NULL,
quote_id int NOT NULL,
product_name varchar(255) NOT NULL,
quantity int NOT NULL,
unit_price decimal(10,2) NOT NULL,
total_price decimal(10,2) NOT NULL,
created_at timestamp NULL DEFAULT CURRENT_TIMESTAMP
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_0900_ai_ci;
MySQL said: Documentation

#1273 - Unknown collation: 'utf8mb4_0900_ai_ci'

==============================

Only Customer in Quote & Click Submit button:

Fatal error: Uncaught mysqli_sql_exception: Unknown column 'created_by' in 'field list' in /home4/yadgui36/jacksbackyardsales.com/inventory-oem/quote.php:85 Stack trace: #0 /home4/yadgui36/jacksbackyardsales.com/inventory-oem/quote.php(85): mysqli->query('INSERT INTO quo...') #1 {main} thrown in /home4/yadgui36/jacksbackyardsales.com/inventory-oem/quote.php on line 85
Resulting Error:

With both Customer & Producted in Quote & Click Submit Button:

Fatal error: Uncaught mysqli_sql_exception: Unknown column 'created_by' in 'field list' in /home4/yadgui36/jacksbackyardsales.com/inventory-oem/quote.php:85 Stack trace: #0 /home4/yadgui36/jacksbackyardsales.com/inventory-oem/quote.php(85): mysqli->query('INSERT INTO quo...') #1 {main} thrown in /home4/yadgui36/jacksbackyardsales.com/inventory-oem/quote.php on line 85

No data added to tables:
quotes
quote_items