Fatal Error on the checkout page when our plugin is activated.

[Chetna1510]

Describe the bug
the checkout page wouldn’t complete the calculation for the form total… it would just be stuck showing a spinning icon. I deactivated the plugin and then the checkout worked fine.

The issue is coming with PHP 8

To Reproduce
The issue is coming with PHP 8 only.

I couldn't replicate this on my site but here are the settings - https://www.dropbox.com/sh/ut9ftsmbrof1l1c/AAB4tTyIHIpyR1sYuAJU7exQa?dl=0

Screenshots
https://prnt.sc/93xnNxegmYM6

Additional context
https://tychesoftwares.freshdesk.com/a/tickets/45176

I checked on client's site and the below error message has been logged -

2022-10-13T14:26:46+00:00 CRITICAL Uncaught TypeError: Unsupported operand types: string - string in /www/petitujo_949/public/wp-content/plugins/checkout-fees-for-woocommerce/includes/class-alg-wc-checkout-fees.php:497
Stack trace:
#0 /www/petitujo_949/public/wp-content/plugins/checkout-fees-for-woocommerce/includes/class-alg-wc-checkout-fees.php(839): Alg_WC_Checkout_Fees->calculate_the_fee(Array, 0, 64, 'fee_1')
#1 /www/petitujo_949/public/wp-content/plugins/checkout-fees-for-woocommerce/includes/class-alg-wc-checkout-fees.php(902): Alg_WC_Checkout_Fees->get_the_fee(Array, 'fee_both')
#2 /www/petitujo_949/public/wp-content/plugins/checkout-fees-for-woocommerce/includes/class-alg-wc-checkout-fees.php(373): Alg_WC_Checkout_Fees->maybe_add_cart_fee(Array)
#3 /www/petitujo_949/public/wp-includes/class-wp-hook.php(307): Alg_WC_Checkout_Fees->add_gateways_fees(Object(WC_Cart))
#4 /www/petitujo_949/public/wp-includes/class-wp-hook.php(331): WP_Hook->apply_filters(NULL, Array)
#5 /www/petitujo_949/public/wp-includes/plugin.php(476): WP_Hook->do_action(Array)
#6 /www/petitujo_949/public/wp-content/plugins/woocommerce/includes/class-wc-cart.php(1885): do_action('woocommerce_car...', Object(WC_Cart))
#7 /www/petitujo_949/public/wp-content/plugins/woocommerce/includes/class-wc-cart-totals.php(272): WC_Cart->calculate_fees()
#8 /www/petitujo_949/public/wp-content/plugins/woocommerce/includes/class-wc-cart-totals.php(833): WC_Cart_Totals->get_fees_from_cart()
#9 /www/petitujo_949/public/wp-content/plugins/woocommerce/includes/class-wc-cart-totals.php(145): WC_Cart_Totals->calculate_fee_totals()
#10 /www/petitujo_949/public/wp-content/plugins/woocommerce/includes/class-wc-cart-totals.php(134): WC_Cart_Totals->calculate()
#11 /www/petitujo_949/public/wp-content/plugins/woocommerce/includes/class-wc-cart.php(1398): WC_Cart_Totals->_construct(Object(WC_Cart))
#12 /www/petitujo_949/public/wp-content/plugins/woocommerce/includes/class-wc-ajax.php(371): WC_Cart->calculate_totals()
#13 /www/petitujo_949/public/wp-includes/class-wp-hook.php(307): WC_AJAX::update_order_review('')
#14 /www/petitujo_949/public/wp-includes/class-wp-hook.php(331): WP_Hook->apply_filters(NULL, Array)
#15 /www/petitujo_949/public/wp-includes/plugin.php(476): WP_Hook->do_action(Array)
#16 /www/petitujo_949/public/wp-content/plugins/woocommerce/includes/class-wc-ajax.php(93): do_action('wc_ajax_update...')
#17 /www/petitujo_949/public/wp-includes/class-wp-hook.php(307): WC_AJAX::do_wc_ajax('')
#18 /www/petitujo_949/public/wp-includes/class-wp-hook.php(331): WP_Hook->apply_filters(false, Array)
#19 /www/petitujo_949/public/wp-includes/plugin.php(476): WP_Hook->do_action(Array)
#20 /www/petitujo_949/public/wp-includes/template-loader.php(13): do_action('template_redire...')
#21 /www/petitujo_949/public/wp-blog-header.php(19): require_once('/www/petitujo_9...')
#22 /www/petitujo_949/public/index.php(17): require('/www/petitujo_9...')
#23 {main}