Problem PHP

Hello,
I have an error message for “Abandoned Amount” and “Rocovered amount” …
It seems that the problem comes from the PHP version, above 7.1.
Cannot have these two digits, here is the error message I got:
“Warning: A non-numeric value encountered in /htdocs/kinic-formation.fr/wp-content/plugins/wc-abandoned-carts-by-small-fish-analytics/admin/charts/class-sfa-abandoned-carts -abandoned-chart.php on line 49 ”
This code seems to be causing the problem: “+ = $ cart-> get_cart_total ();”
Do you also have this concern?
Is there a solution?
thank you in advance
Best regards