VAT-Validation: Uncaught TypeError: explode()

Hello,
I want to switch from another VAT-plugin that will be deprecated soon.
Installation of your plugin was without an error and I didn’t change anything in the settings. On every VAT-validation on the checkout-page I’m receiving this error:

PHP Fatal error: Uncaught TypeError: explode(): Argument #2 ($string) must be of type string, array given in /var/www/vhosts/hbmedia.info/dev.petpla.net/wp-content/plugins/eu-vat-for-woocommerce/includes/functions/alg-wc-eu-vat-functions-validation.php:229

Stack trace:

#0 /var/www/vhosts/hbmedia.info/dev.petpla.net/wp-content/plugins/eu-vat-for-woocommerce/includes/functions/alg-wc-eu-vat-functions-validation.php(229): explode()
#1 /var/www/vhosts/hbmedia.info/dev.petpla.net/wp-content/plugins/eu-vat-for-woocommerce/includes/class-alg-wc-eu-vat-ajax.php(94): alg_wc_eu_vat_validate_vat()
#2 /var/www/vhosts/hbmedia.info/dev.petpla.net/wp-includes/class-wp-hook.php(307): Alg_WC_EU_VAT_AJAX->alg_wc_eu_vat_validate_action()
#3 /var/www/vhosts/hbmedia.info/dev.petpla.net/wp-includes/class-wp-hook.php(331): WP_Hook->apply_filters()
#4 /var/www/vhosts/hbmedia.info/dev.petpla.net/wp-includes/plugin.php(474): WP_Hook->do_action()
#5 /var/www/vhosts/hbmedia.info/dev.petpla.net/wp-admin/admin-ajax.php(187): do_action()

We are using WordPress 5.9.2.

Best regards
Felix