Hello and have nice day. there is an problem with wallet top up in plugin

my customers can not charge their wallet and when they want to do it , they receive “Sorry, this product cannot be purchased” in their cart .

also my debugs shows this errors:
Warning: Trying to access array offset on value of type null in /home/fatemehtestalfa/public_html/wp-content/plugins/woo-wallet/includes/class-woo-wallet-widgets.php on line 42
Warning: Trying to access array offset on value of type null in /home/fatemehtestalfa/public_html/wp-content/plugins/woo-wallet/includes/class-woo-wallet-widgets.php on line 61

I’ll be appreciate if help me 🌸