Could not initialize class org.eclipse.persistence.jaxb.BeanValidationHelper while trying to get JSON response

This is a bug in Glassfish: https://github.com/javaee/glassfish/issues/21440 It probably won't be fixed, you should switch to http://www.payara.fish/ which is patched and updated version of Glassfish (has even commercial support if needed).

This bug is fixed in Payara.