I am not able to enter this formula into the data validation in order to
allow a user to only enter text. any suggstions?

=SUMPRODUCT(--(ISNUMBER(MATCH(CODE(MID(A1,ROW(INDIRECT("1:"&LEN( A1))),1)),ROW(INDIRECT("97:122")),0))))+SUMPRODUCT (--(ISNUMBER(MATCH(CODE(MID(A1,ROW(INDIRECT("1:"&LEN( A1))),1)),ROW(INDIRECT("65:90")),0))))=LEN(A1)