I believe there should be a possibilty for an unknown signer to exist in a Package, here’s a use case from my company:
A truck driver must deliver concrete to a construction zone and the person who receives the concrete must sign as well as the driver. The driver is known beforehand as he is from our company so all is fine there but the person in the construction zone is an unknown until the moment we arrive there.
The current workaround is having a “ghost signer” with basically empty FirstName, LastName, and Email. And in the document itself there is a field where the signer can input his name. This is clearly not ideal.
A custom integration would handle this scenario as you’d be able to collect that information before creating the transaction.
But if you are not able to use custom integration, the current capability to handle this is to use the “change signer” feature that allows you to specify a signer and have that signature reassigned to the appropriate person from within the ceremony, which might be something you can use to improve your process.
On top of that, I will put in an enhancement request on your behalf and email support to input the ER based on this post.