Are you 100% sure the expression returns a value?
Try disabling the send mail step and add a set value step, having the same expression and Output enabled. Do you see anything returned in the dev tools when you submit the form then?
Also, it’s wrong to put the Setup Mailer step in the server action. It must be defined under Globals > Mailer. So remove it from the server action and define it there:
Setup Mailer was already in Globals so just removed from Server action, thanks for the tip.
Putting a static email address in the from and return worked. Deleted form and created new input fields but this time did not use the copy facility and added them individually from the Add New Component menu.
Form now sends OK.
Not sure i understand what you mean here, but obviously your form input name/id was different than the one you used under POST. So you could have just compared them, instead of recreating everyting.