FFCacheManager.php on line 358

Hi, i have an error:

Deprecated: The behavior of unparenthesized expressions containing both ‘.’ and ‘+’/’-‘ will change in PHP 8: ‘+’/’-‘ will take a higher precedence in /home/hotelsameland/domains/hotelsameland.nl/public_html/wp-content/plugins/flow-flow/includes/cache/FFCacheManager.php on line 358

When i google this, i saw that a lot of sites have this problem.
https://www.google.com/search?q=FFCacheManager.php+on+line+358&oq=FFCacheManager.php+on+line+358&aqs=chrome..69i57&sourceid=chrome&ie=UTF-8

Any idea how to fix this?
Thanks

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