Error message: This field can only contain numeric values

Im having issues with one of my forms where its coming up with an error message "This field can only contain numeric values" The field is part of the credit card details asking for the expiry month and only gives the option of the month name but wont accept it. My client is having trouble with it and I have also tried with her credit card details and it wont work. However I did a test with my credit card details and it worked. Not sure why it wont accept her details in the month field.

Thanks 

I cloned your form and I was able to replicate the issue. Please delete the "$" in the Suggested Amount of the Payment field. Here's a screenshot:

I hope this helps. If you need further assistance, please contact us again.

Thanks John :)