Error in call isValidNumber by mb_strcut from namespace libphonenumber

[enrisca]

Attempted to call function "mb_strcut" from namespace "libphonenumber".","error":"#0 /home/enrsica/Proyectos/edigitaltrust/crm-leads-api-core/vendor/giggsey/libphonenumber-for-php/src/Matcher.php(96): libphonenumber\Matcher->doMatch('lookingAt')\n#1 /home/enrsica/Proyectos/edigitaltrust/crm-leads-api-core/vendor/giggsey/libphonenumber-for-php/src/RegexBasedMatcher.php(50): libphonenumber\Matcher->lookingAt()\n#2 /home/enrsica/Proyectos/edigitaltrust/crm-leads-api-core/vendor/giggsey/libphonenumber-for-php/src/RegexBasedMatcher.php(37): libphonenumber\RegexBasedMatcher->match('666666666', '[5-9]\\d{8}', false)\n#3

Help, what could be happens?
thanks!!

[janjango]

I just solve this issue by running sudo apt-get install php-mbstring on Ubuntu 16.04