Once the cap is reached, new articles can no longer be published open access free of charge under the deal. In that case, the author must cover the open access publishing costs themselves.
To avoid unexpected expenses, the university libraries (UKB) and Universities of the Netherlands (UNL) advise authors to use the Rights Retention Strategy (RRS) when submitting to journals that are part of a capped deal.
If your article is accepted after the cap has been reached, the RRS still allows you to meet the open access requirements of your funder. You can do this by uploading the author-accepted manuscript (AAM) to the Radboud Repository.
You can find an overview of all publisher deals on the open access website. Deals that include a cap are marked with the label “Attention: capped deal!”.