Basically, something is broken while attempting to install SVN module for PHP via “Modules installer” option. To manually install extension follow these steps:

1. Download the SVN PECL package:

   wget pecl.php.net/get/svn-1.0.3.tgz

2. Extract the package:

   tar xzf svn-1.0.3.tgz

3. Run phpize for appropriate PHP version:

   /opt/cpanel/ea-php56/root/usr/bin/phpize

4. Configure with appropriate PHP configuration:

   ./configure --with-php-config=/opt/cpanel/ea-php56/root/usr/bin/php-config

5. Edit the Makefile to add following CFLAGS:

   CFLAGS = -g -O2 -std=c99

6. Compile and install extension:

   make
   make install

7. Create configuration for SVN extension:

   vi /opt/cpanel/ea-php56/root/etc/php.d/svn.ini

   and add the following:

   ; Enable svn extension module
   extension=svn.so