How to get a pinentry box to digitally sign all emails

[Sharon Kimble <boudiccas@skimble.plus.com>]

One of the things that I really miss in emacs-27 is the inability to be
able to digitally sign all my emails just before they are sent.

Back in emacs-26 I had this code which called the pinentry box

  --8<---------------cut here---------------start------------->8---
(add-hook 'gnus-message-setup-hook 'mml-secure-message-sign-pgp)
(add-hook 'message-setup-hook 'mml-secure-message-sign-pgp)
  --8<---------------cut here---------------end--------------->8---

But with emacs-27 that same code brings this response

  --8<---------------cut here---------------start------------->8---
Debugger entered--Lisp error: (error "Couldn’t find any signer names.")
  signal(error ("Couldn’t find any signer names."))
  error("Couldn't find any signer names%s" ".")
  mml-secure-epg-sign(OpenPGP clear)
  mml1991-epg-sign((part (sign . "pgp") (tag-location . 292) (contents . "\n-- \nA taste of linux = http://www.sharons.org.uk\n...")))
  mml1991-sign((part (sign . "pgp") (tag-location . 292) (contents . "\n-- \nA taste of linux = http://www.sharons.org.uk\n...")))
  mml-pgp-sign-buffer((part (sign . "pgp") (tag-location . 292) (contents . "\n-- \nA taste of linux = http://www.sharons.org.uk\n...")))
  mml-generate-mime-1((part (sign . "pgp") (tag-location . 292) (contents . "\n-- \nA taste of linux = http://www.sharons.org.uk\n...")))
  mml-generate-mime(nil nil)
  message-encode-message-body()
  message-send-mail(nil)
  message-send-via-mail(nil)
  message-send(nil)
  message-send-and-exit(nil)
  funcall-interactively(message-send-and-exit nil)
  call-interactively(message-send-and-exit)
  orgtbl-ctrl-c-ctrl-c(nil)
  funcall-interactively(orgtbl-ctrl-c-ctrl-c nil)
  call-interactively(orgtbl-ctrl-c-ctrl-c nil nil)
  command-execute(orgtbl-ctrl-c-ctrl-c)
  --8<---------------cut here---------------end--------------->8---
  
So how do I call the pinentry box in emacs-27 please?

Thanks
  Sharon.  
-- 
A taste of linux = http://www.sharons.org.uk
TGmeds = http://www.tgmeds.org.uk
DrugFacts = https://www.drugfacts.org.uk
Debian 10.2, fluxbox 1.3.7, emacs 27.0.90, org 9.3.6