I recently had a problem validating a number field to prevent the user from sending text instead of a number. So I found this solution that is working for me so far.
As any number is divisible by 1, the result will always be true, but when adding a letter the result will be false.
I took this test. I copied a string from a notepad and pasted it into the field in the live test and it actually pasted normally. I don’t know if it could be a bug in the thunkable, but in the test, it pasted the string.