Can' install parrot-sphinx under Ubuntu 20.04 LTS: repo is not signed

Installing parrot by instruction here:

However got errors:

$ echo "deb `lsb_release -cs`/" | sudo tee /etc/apt/sources.list.d/sphinx.list

deb focal/

$ sudo apt-key adv --keyserver --recv-keys 508B1AE5
Executing: /tmp/apt-key-gpghome.REPYP0Fez8/ --keyserver --recv-keys 508B1AE5
gpg: key 47727EDC508B1AE5: public key "Samuel Lekieffre <>" imported
gpg: Total number processed: 1
gpg:               imported: 1

$ sudo apt update
Err:5 focal/ InRelease                                                                  
  403  Forbidden [IP: 80]
Reading package lists... Done
E: Failed to fetch  403  Forbidden [IP: 80]
E: The repository ' focal/ InRelease' is not signed.
N: Updating from such a repository can't be done securely, and is therefore disabled by default.
N: See apt-secure(8) manpage for repository creation and user configuration details.

This solution: Sphinx on ubuntu 19.04 does not work as 20.04 has libboost1.71 while parrot for bionic requires libboost1.65.1 and qt4 which is not available.

Any ideas or wait for release for 20.04?

Need 20.04 however it contains newer packages, so old one does not install.