Search notes:

ORA-01839: date not valid for month specified

April has only 30 days, the following statement throws ORA-01839: date not valid for month specified: 
select
   to_date('2021-04-31', 'yyyy-mm-dd') hmmm
from
   dual;

NUMTOYMINTERVAL

The following statement runs without problems … 
select
   date '2021-02-01' + numtoyminterval(1, 'month')
from
   dual;
… but this one throws ORA-01839: date not valid for month specified 
select
   date '2021-01-31' + numtoyminterval(1, 'month')
from
   dual;

See also

The date datatype
ORA-01843: not a valid month
Other Oracle error messages

Index

Fatal error: Uncaught PDOException: SQLSTATE[HY000]: General error: 8 attempt to write a readonly database in /home/httpd/vhosts/renenyffenegger.ch/php/web-request-database.php:78 Stack trace: #0 /home/httpd/vhosts/renenyffenegger.ch/php/web-request-database.php(78): PDOStatement->execute(Array) #1 /home/httpd/vhosts/renenyffenegger.ch/php/web-request-database.php(30): insert_webrequest_('/notes/developm...', 1758206669, '216.73.216.150', 'Mozilla/5.0 App...', NULL) #2 /home/httpd/vhosts/renenyffenegger.ch/httpsdocs/notes/development/databases/Oracle/errors/ORA-01839_date-not-valid-for-month-specified(62): insert_webrequest() #3 {main} thrown in /home/httpd/vhosts/renenyffenegger.ch/php/web-request-database.php on line 78