Module is broken since its migration as the hooks used for reconciliation
are not used anymore in Odoo 12.0.
Therefore transaction_ref is dropped from account.move.line and transaction_id
is now written into account.move.ref at invoice validation to allow the use
of standard Odoo mechanism in the reconciliation process.
As Odoo defined invoice_payment_ref on account.move in v13.0, avoiding extra
fields in v12.0 is already a step in the right direction.