target="_blank" not working in Wysiwyg feild

[inshaal]

can any one tell i am sending <a href='https://web.whatsapp.com/send?phone=$phn);' target="_blank" class="opennewtab">WhatsApp</a> tag through api to "Wysiwyg" which working fine but when i am using target="_blank" its not working i have also tried adding javascript but dont know exactly where i can add javascript or add custom code to my leads backned