PUSHBullet API Integration with suitecrm

Hi every one, I am simply writing this line
$pushbullet = new PHPushbullet\PHPushbullet(‘account token’);
but this is giving me error. Although I have run it in my localhost simple php. Its working fine but in suitecrm it is causing trouble.

It gives php fatal error: Uncaught Error: Class ‘PHPushbullet’ not found in /var/www/html/custom/modules/Cases/pushbullet/cstmMailsCls.php:75\nStack trace:\n#0 /var/www/html/include/utils/LogicHook.php(262): cstmMailsCls->cstmMailsFunc(Object(aCase), ‘after_save’, ‘’)\n#1 /var/www/html/include/utils/LogicHook.php(199): LogicHook->process_hooks(Array, ‘after_save’, ‘’)\n#2 /var/www/html/data/SugarBean.php(3118): LogicHook->call_custom_logic(‘Cases’, ‘after_save’, ‘’)\n#3 /var/www/html/data/SugarBean.php(2434): SugarBean->call_custom_logic(‘after_save’, ‘’)\n#4 /var/www/html/custom/modules/Cases/pushbullet/cstmMailsCls.php(44): SugarBean->save()\n#5 /var/www/html/include/utils/LogicHook.php(262): cstmMailsCls->cstmMailsFunc(Object(aCase), ‘after_save’, ‘’)\n#6 /var/www/html/include/utils/LogicHook.php(199): LogicHook->process_hooks(Array, ‘after_save’, ‘’)\n#7 /var/www/html/data/SugarBean.php(3118): LogicHook->call_custom_logic(‘Cases’, ‘after_save’, ‘’)\n#8 /var/www/html/data/SugarBean.php(2434): SugarBean->call_custom_logic(‘after_save’, ‘’)\n#9 in /var/www/html/custom/modules/Cases/pushbullet/cstmMailsCls.php on line 75, referer: https://crm.ippbx.com/index.php?action=ajaxui

This line is working well in simple php but not in suitecrm $pushbullet = new PHPushbullet\PHPushbullet(‘account token’);.
In simple php the bolded words changes color to blue but not in suitecrm.