I want to know if a free plan MySQL service cannot be connected by a Spring Boot application

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Access denied for user ‘root’@‘***’ (using password: YES)

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Hey @1_1 I am not aware of any reason why you should not be able to connect to MySQL from springboot.

Have you tried confirming credentials outside of the springboot application?
We have documentation on it here.

or use a tool like Connect to Aiven for MySQL® with MySQL Workbench | Aiven docs