It seems that there is no option to make the product field a required field?
This means that if a user defined price is asked for and if the customer then forgets to enter an amount into this field, the form still can be sent.
Would be good to have this feature in a next release.
It would also be good if a minimum or maximum amount could be set for the user defined price and also that anything entered here is checked for validity (numbers only).
Thanks!