What constraints are there with creating an integrated menu? (validations)

Square POS supports the concept of 'global options'. This means that any option set created in your Square POS can be used with any item, and Square does not validate the combination. Square will accept what is sent through in the order. 

Global options allow a great deal of freedom when creating an integrated App menu. However, care must be taken to ensure that you don't link inappropriate option sets with items. For example, it is possible to configure a menu where a can of soft drink can be ordered with a preparation type of 'rare'.