Yes, since eligibility for the funding provided by the Oxford University Press (OUP) Read & Publish agreement is confirmed as part of the OUP manuscript submission process, it is necessary to have completed your article in order to be covered by the agreement.
Funding cannot be provided in advance of an article being written or completed.
However, if you are not at the stage of submitting a completed manuscript, but would like to discuss the agreement and how to ensure your eligibility, please email: openaccess@qub.ac.uk