SSH to your server and run the following commands:
yum install gmp-devel
cd /usr/local/directadmin/custombuild
mkdir -p custom/fpm
cp -fp configure/fpm/configure.php71 custom/fpm/configure.php71
Then add --with-gmp
line to the end of the custom/fpm/configure.php71 file.
Finally, build php:
./build php n
Restart apache.
source: https://help.directadmin.com/item.php?id=252&in3=--with-gmp&in1=fpm&in2=configure.php71