Date time zone issue

todatetime() expects an input string formatted presumably in your given time zone's format.  if you changed your user locale but didn't update the formatting of the string you're passing it, then most likely it's now getting a string that it doesn't understand the formatting for.

I can't give much more specific advice than that since you haven't included your actual code and haven't included the source for the date/time string you're trying to pass into "todatetime()", both of which are important for figuring out what you'd need to change here.

if(
rule!P3_utils_checkIsNullOrEmpty(ri!dateTime),
{},
text(todatetime(ri!dateTime),cons!FORMAT_DATE_TIME),
)

ri!dateTime is anytype 
cons!FORMAT_DATE_TIME - dd/mmm/yyyy hh:mm z

here actually I am passing date as text. I am fetch it from json

if(
rule!P3_utils_checkIsNullOrEmpty(ri!dateTime),
{},
text(todatetime(ri!dateTime),cons!QST_FORMAT_DATE_TIME),
)

cons!QST_FORMAT_DATE_TIME - dd/mmm/yyyy hh:mm z

datetime variable is any type.

and the main thing is we are passing date as text. We are fetching it from JSON.

What do you mean with "fetching in from JSON"?

If I do a fromJson() on a correctly formatted datetime JSON value, Appian returns me a dateTime value.

i did a!fromjson
the value is "9/30/2025 9:30 AM AKDT",
i changed the locale of my system. and it was breaking. did you changed the locale ?

Is that the value in the JSON, or the return of fromJson()?

This is a datetime value according to ISO 8601. Any other format is "garbage" and you have to parse it manually.

fromjson

Is this rule expecting to receive a dictionary (which is what you're passing it here), as opposed to a bare DateTime value?