When you connect Microsoft Dynamics 365 Business Central, Microsoft may tell you that Kolleno needs an administrator's approval. Many Microsoft tenants do not let ordinary users approve an app on their own, so this has nothing to do with your Business Central permissions. You cannot get past that screen yourself, and the approval link below is how you pass the decision to someone who can.
In that case, go to Settings > Accounting and click Copy admin approval link on the Business Central row.
Send that link to whoever administers your Microsoft tenant and ask them to approve Kolleno on behalf of the organization. They only need to do this once for the whole company.
Next steps
Once your admin confirms they have approved it, go back to Settings > Accounting and click Connect on Business Central. Sign in with the Business Central account whose data Kolleno should read, and pick it carefully if you are signed in to more than one Microsoft account.
Approval is separate from the Kolleno Business Central extension. If you have not installed that yet, see How to install a Business Central extension.