Please share all of your code and describe where and how the email is being initiated.
Ok consider this as a complete PLSQL page-level process i am working on with single line as below its correct and will run, it executes on click of a button.
P_TO => 'firstname.lastname@example.org' ,
P_FROM =>'email@example.com' ,
P_CC => 'firstname.lastname@example.org' ,
P_BCC => '',
P_BODY => body text,
P_SUBJ => 'This is my text mail',
P_BODY_HTML => '<b>Hello we are testing the email body here</b>');
when others then null;