Answers for "Unknown collation: 'utf8mb4_0900_ai_ci'"

Unknown collation: 'utf8mb4_0900_ai_ci'

I believe this error is caused because the local server and live server are running different versions of MySQL. To solve this:

Open the sql file in your text editor
Find and replace all utf8mb4_unicode_520_ci with utf8mb4_unicode_ci
Save and upload to a fresh mySql db

unknown collation: 'utf8mb4_0900_ai_ci' stackoverflow

ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_unicode_520_ci;
replace with
ENGINE=InnoDB DEFAULT CHARSET=utf8 COLLATE=utf8_general_ci;

Unknown collation: 'utf8mb4_0900_ai_ci'

search utf8mb4 change with utf8 
search utf8mb4_unicode_ci change with utf8_unicode_ci