Yes, both the invoice supplying organisation and the invoice receiving organisation need to be on LUCA Plus.
LUCA Plus requires access to both supplier and customer accounting solutions in order to capture and synchronise invoices between accounting software. If the supplying organisation is not using LUCA Plus, invoices cannot be pulled from their accounting solution when an invoice is sent. Make sure the supplying organisation is using LUCA Plus and try again.
To invite others to use automatic invoice processing (e-invoicing), see Inviting others to LUCA Plus