ORA-904 on statement

We have a 19.19 on Linux and the Alert.log is gving parse errors for some statements. They're all quite similar, and custom made. Below is one example of such a statement. They all eturn ORA-904 error codes. My main concern is the use of colon-parameters. I shouldn't be seeing those, should I ? I mean, they should have been parsed, or the statement not run. Right ?

An example statement:

select 'x'

from dual

where :1 is not null

and 2: is not null

and 3: is not null

and 4: is not null

and some_pkg.some_check(:5,:6,:7,'XX') = 7

and '' = 'U'

and some_other_pkg.some_get(:10) = 'KK'