It is recommended to register your own client ID as instructed on Registratie Exact Online app voor gebruik met Invantive Control for Excel (only in Dutch, I am sorry). Essentially, this enable use of your own Exact Online app.
Further, you will need to upgrade to a recent 20.2 production release, such as 20.2.27 or newer, as found on https://releasenotes.invantive.com.
That will solve the log on issue.
For the near future, Exact and Invantive will change their partnership to provide large accounting firms and customers in general with more flexibility while maintaining our view on how to best implement security according to ISO 2700[12] and the OAuth standard.