Account report does not show any data

I've linked projects to Tempo Accounts, but the Account report does not display any data. What do I do?

Only linking an Account to a project will not set the Account custom field on existing issues. It only means that any issue in this project can be credited to a specific Account [available from the list of linked Accounts], and this is done by setting the desired Account in the Account Custom field in the Issue View.

This article explains, step-by-step, how to link Accounts to issues.