Cannot modify header information

Hello there,

instead of my admin login page, I see these error messages associated with Sonaar Music Player:
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Warning: array_key_exists() expects parameter 2 to be array, string given in /homepages/45/d4295164981/htdocs/dominik-matzka.de/wp-content/plugins/mp3-music-player-by-sonaar/admin/class-sonaar-music-admin.php on line 1295

Warning: Cannot modify header information - headers already sent by (output started at /homepages/45/d4295164981/htdocs/dominik-matzka.de/wp-content/plugins/mp3-music-player-by-sonaar/admin/class-sonaar-music-admin.php:1295) in /homepages/45/d4295164981/htdocs/dominik-matzka.de/wp-includes/pluggable.php on line 1340

Warning: Cannot modify header information - headers already sent by (output started at /homepages/45/d4295164981/htdocs/dominik-matzka.de/wp-content/plugins/mp3-music-player-by-sonaar/admin/class-sonaar-music-admin.php:1295) in /homepages/45/d4295164981/htdocs/dominik-matzka.de/wp-includes/pluggable.php on line 1343

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The plugin works well, by the way. However, can you tell me how to get rid of these annoying messages? I’ve tried to troubleshoot them myself using this link – https://wordpress.org/support/article/faq-troubleshooting/#top –
but wasn’t able to identify any “spaces, new lines, or other stuff” in line 1295.
This is the code from line 1295:

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if( array_key_exists(‘artist_of_album’, $meta) ){ //If album post has been created by sonaar theme
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Thanks a lot in advance!

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