Error in Vaild if function when avoiding duplicate

[rishabh3vs]

I'm currently facing an issue with the Valid If condition in my AppSheet app.

Objective: I have a table in my app called "Client List," and I'm trying to enforce uniqueness for the "Contact No." column. I want to ensure that the contact number is 10 digits long and that it's unique across all rows, excluding the currently edited row.

I tried following codes

Code1

AND( LEN([Contact No.]) = 10,
         ISBLANK(
                  FILTER ("Client List", AND(
                                               [Contact No.] = [_THIS],
                                                 NOT([_ROWNUMBER] = [_THISROW].[Client Name])))))

Code 2
AND( LEN([Contact No.]) = 10,
            ISBLANK( FILTER(Client List, ([_THIS] = [Contact No.])) - LIST([_THISROW])))

Issue:  The formula seems to work initially, but I encounter an error when trying to edit an existing row. It appears that the current row is not being excluded properly during the validation check.

Additional Details:

• I do have a key column named "[Client Name]" in my "Client List" table.
• I've tested the formula, and it works as expected for new entries but not during the editing process.

 Question:

1. Can anyone spot any issues in the provided formula?
2. Is there a better approach to achieving uniqueness for the "Contact No." column while editing existing rows?

I appreciate any insights or suggestions the community can provide. Thank you in advance for your help!