When you are entering the names of Facebook Forms into Marketo Triggers, Filters, and/or other fields, Marketo may present an error (red-squiggle) under the name value, stating that the value is invalid.
The reason that Marketo states this value is invalid is because the Facebook Form has not yet been filled out for the first time. Only after an existing Marketo Record has filled out the Facebook Form will the Name Value of the form be in the Marketo system.
If you were interested in setting up a Trigger Campaign to trigger off Facebook Form fillouts, you would first have to fill out the form with a test record that exists in the Marketo Lead Database. If the situation was within a Batch Campaign, or entering the Form Name in any other fields, the same resolution would apply: fill out the form with a test record that you are associated with in the Marketo Lead Database.