Unable to update packages via apt-get on Plesk server: all InRelease doesn't support architecture 'amd64'

Symptoms

• Updating packages via apt-get update produces the following error:

  # apt update
  ...
  ...
  N: Skipping acquire of configured file 'all/binary-amd64/Packages' as repository
  'http://autoinstall.plesk.com/pool/WPB_18.0.51_64 all InRelease' doesn't
  support architecture 'amd64'.

Cause

Unsupported package repository configuration.

Resolution

1. Connect to the server via SSH.

2. Edit the repository file /etc/apt/sources.list.d/plesk.list. Vi editor can be used for this.

3. Modify the repository line from the error to add arch=i386 as follows:

   Before:

   CONFIG_TEXT: deb [signed-by=/etc/apt/keyrings/plesk.gpg] http://autoinstall.plesk.com/pool/WPB_18.0.51_64/ all all

   After:

   CONFIG_TEXT: deb [arch=i386 signed-by=/etc/apt/keyrings/plesk.gpg] http://autoinstall.plesk.com/pool/WPB_18.0.51_64/ all all

4. Update packages once again:

   # apt-get update