Text box field not accepting alphanumeric characters

I am using text field with conditions to enable a secure form using clients own telephone numbers. My problem is where (for an instance) you may have a situation where two or more people share the same telephone number, a simple way around this would to include for and instance an F after the number indicating that it is the female partner and M for the male counterpart, I have no problem with conditions the problem lies with the field that I am using for the the secure form activation as it wont allow alphanumeric characters and I cant seem to find a way of altering.

any advice on this be most welcome

I believe that you are referring to the Identification code field in your JotForm. I see that this field is a number field and hence it is not accepting any alphabets. 

Please replace this field with a text box field from Form Tools section so that it should be accepting alphanumeric characters.

Hope this information helps! Please get back to us if you need any further assistance. We will be happy to help.