error when using httpuritype( 'http://www.oracle.com' ).getBlob();

Dears,

Can you please advise how to solve the below error when using httpuritype( 'http://www.oracle.com' ).getBlob():

ORA-29273: HTTP request failed

ORA-06512: at "SYS.HTTPURITYPE", line 73

ORA-06512: at "SYS.UTL_HTTP", line 1288

ORA-29024: Certificate validation failure

ORA-06512: at "SYS.UTL_HTTP", line 651

ORA-06512: at "SYS.UTL_HTTP", line 1278

ORA-06512: at "SYS.HTTPURITYPE", line 60

ORA-06512: at line 4

ORA-06512: at "SYS.DBMS_SQL", line 1721

Thanks in advance

Murad