C7837wip can't add visitor user

In web Client users setting I can't increase operator or visitor user when i put password it shows "The length of the password must be greater than or equal to 8 and the letters or numbers." but my password is more than 8 and have letters and number sure. my firmware 48.53.75.120

Dear Sir/Madam,
Thanks for your message, you are advised reset camera to fatory settings,the password will return to 888888.

the password change into 88888, it will be more easier to break

geraldinehagen replied at 2020-4-14 02:08
the password change into 88888, it will be more easier to break

Hi， Sir/Madam,
In fact, you can setup a new password,  for examle, like  Tsdde3434232.
password could including letters, numbers.