kjdelys PRO said 10 months ago on Active Storage Validators :
Hey,
file_size_validator won't work with has_many_attached.

You need to update it to something like

if value.class == ActiveStorage::Attached::Many
  return if value.all? { |file| file.blob.byte_size < options[:less_than].megabytes }
else
  return if value.blob.byte_size < options[:less_than].megabytes
end