the requested php extension ext-gmp * is missing from your system ubuntu code example

Example: Missing BC Math or GMP extension.

To install GMP for PHP7.0 on Ubuntu, 
run: sudo apt-get install php-gmp

Restart apache : sudo service apache2 restart

Make sure your php.ini contains the following: extension=php_gmp.so

To find out where your php.ini is located, run: php --ini