Fatal error after latest update 5.5

After updating your contact form7 plugin to version 5.5 our wordpress site crashes and gives a fatal error. Rollback to previous contact form 7 version 5.4.2 restores site. Debug shows this error:

Parse error: syntax error, unexpected ‘namespace’ (T_NAMESPACE), expecting identifier (T_STRING) in /wp-content/plugins/contact-form-7/includes/rest-api.php on line 15 Notice: is_embed was called incorrectly. Conditional query tags will not work until the query has been run. For this, it always returns ‘false’.

WordPress version 5.8.1

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