Different issues related to Enums on PHP7

[maurogesuitti]

Summary

The requirement for the latest version of this package is "PHP 7.3 and later" but PHP 7.X doesn't support Enums so I am getting errors on serialization.

Expected Behavior

The package should work normally on PHP 7 or the requirement should be different.

Current Behavior

syntax error, unexpected 'PostcardSize' (T_STRING)

PostcardSize is an Enum

Steps to Reproduce

(new LettersApi($config, $guzzleClient))->create(new LetterEditable($data));

--> Exception: syntax error, unexpected 'PostcardSize' (T_STRING)
--> /var/www/vendor/lob/lob-php/lib/ObjectSerializer.php:93
--> FYI: $data['size'] === "4x6";

Context (Environment)

• I got the same exception with any API method that uses Enums.
• I am using PHP 7.4.6 and Laravel 6.
• If there is another way to use the library that works on PHP 7 that would be awesome.