Issue Creating Headers

I’m trying to add some headers via the Site>HTTP Headers area and keep running into this 500 error:

Plugin: 5.3.6 4.2
WordPress: 6.1.1 (single)
PHP: 8.0.25
Browser: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_7) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/107.0.0.0 Safari/537.36
JavaScript: https://XXXX.wpengine.com/wp-content/plugins/redirection/redirection.js?ver=5.3.6-16d9cc72e7ac56bb977b78fce03e6ba0
REST API: https://XXXX.wpengine.com/wp-json/
Query: ?page=redirection.php&sub=site

I turned on debug logging and found this:

[19-Dec-2022 18:07:20 UTC] PHP Warning:  Array to string conversion in /nas/content/live/XXXX/wp-content/plugins/redirection/models/header.php on line 108
[19-Dec-2022 18:07:20 UTC] PHP Fatal error:  Uncaught TypeError: iconv(): Argument #3 ($string) must be of type string, array given in /nas/content/live/XXXX/wp-content/plugins/redirection/models/header.php:115
Stack trace:
#0 /nas/content/live/XXXX/wp-content/plugins/redirection/models/header.php(115): iconv('UTF-8', 'UTF-8//IGNORE', Array)
#1 /nas/content/live/XXXX/wp-content/plugins/redirection/models/header.php(25): Red_Http_Headers->sanitize(Array)
#2 [internal function]: Red_Http_Headers->normalize(Array)
#3 /nas/content/live/XXXX/wp-content/plugins/redirection/models/header.php(8): array_map(Array, Array)
#4 /nas/content/live/XXXX/wp-content/plugins/redirection/redirection-settings.php(223): Red_Http_Headers->__construct(Array)
#5 /nas/content/live/XXXX/wp-content/plugins/redirection/api/api-settings.php(117): red_set_options(Array)
#6 /nas/content/live/XXXX/wp-includes/rest-api/class-wp-rest-server.php(1171): Redirection_Api_Settings->route_save_settings(Object(WP_REST_Request))
#7 /nas/content/live/XXXX/wp-includes/rest-api/class-wp-rest-server.php(1018): WP_REST_Server->respond_to_request(Object(WP_REST_Request), '/redirection/v1...', Array, NULL)
#8 /nas/content/live/XXXX/wp-includes/rest-api/class-wp-rest-server.php(442): WP_REST_Server->dispatch(Object(WP_REST_Request))
#9 /nas/content/live/XXXX/wp-includes/rest-api.php(410): WP_REST_Server->serve_request('/redirection/v1...')
#10 /nas/content/live/XXXX/wp-includes/class-wp-hook.php(308): rest_api_loaded(Object(WP))
#11 /nas/content/live/XXXX/wp-includes/class-wp-hook.php(332): WP_Hook->apply_filters('', Array)
#12 /nas/content/live/XXXX/wp-includes/plugin.php(565): WP_Hook->do_action(Array)
#13 /nas/content/live/XXXX/wp-includes/class-wp.php(399): do_action_ref_array('parse_request', Array)
#14 /nas/content/live/XXXX/wp-includes/class-wp.php(780): WP->parse_request('')
#15 /nas/content/live/XXXX/wp-includes/functions.php(1332): WP->main('')
#16 /nas/content/live/XXXX/wp-blog-header.php(16): wp()
#17 /nas/content/live/XXXX/index.php(17): require('/nas/content/li...')
#18 {main}
  thrown in /nas/content/live/XXXX/wp-content/plugins/redirection/models/header.php on line 115

Not sure where to go from here.