Hi, I am using masking for a text field to restrict it to 16 characte

You could have a message under "Required message". Does that suffice your requirement?

Why are you masking? Can you not set a validation instead? See "Editable Grid with Validations." forum.appian.com/.../SAIL_Components.html

its a portal version I am using, I tried JS validation dint work properly because its dynamic , e.g, if I have two rows Number from the image above, if I have validation max char 16, its taking total number of characters from both rows since the field id is the same for both rows, if I can modify the message thrown by masking i.e ("input format incorrect") that would help

If you cannot change the error message, you could have the validations set a flag if they catch an error and use that flag as the condition for an if which shows the error you want.

You can use validation message for this. a!validationmessage() is OOB functionality.
Refer: forum.appian.com/.../SAIL_Components.html

You can use a JS function in the validation field instead of the masking field and then configure the validation message.

I created a JS function to limit the length of a text field in a portal grid about two years ago. The text file includes the function and how to call it for validation.

grid field length validation.txt

You can also create a function like this :

function verifyMaxLength(fieldToCheck, sizeMax) {

          var textToCheck = FormAPI.getValue(fieldToCheck).id;

if (textToCheck.length > sizeMax)
return (false);
else
return (true);
}
And call it in the validation field like this : return verifyMaxLength('text23', 16); ('text'23' is the id of the field)
Of course you can adatp it to check for a min value.

My bad I didn't see you comment ! And by the way you showed me an issue !! We have a similar use case (a dynamic grid with a text limitation). We are using a JS function in validation field and we never saw this issue yet but yes ! It did work if I have two rows.
So I think the Jared's solution is the best. I'll try it.

It didn't work*