Its going to look something like this:
DECLARE
l_resp_body CLOB;
BEGIN
l_resp_body := apex_web_service.make_rest_request(
p_url => 'https://api.textlocal.in/docs/sendsms',
p_http_method => 'POST',
-- p_username => '<username>',
-- p_password => '<password>',
p_parm_name => APEX_UTIL.string_to_table('apikey:numbers:sender:message'),
p_parm_value => apex_util.string_to_table('val1:val2:val3:val4')
);
DBMS_OUTPUT.PUT_LINE (apex_web_service.g_status_code);
DBMS_OUTPUT.PUT_LINE (dbms_lob.substr(l_resp_body, 32000,1));
END;
/