Hello. Please make sure that the domain in question is in the renewal grace period. This is the help file/instructions on how to renew or get back your domain. https://www.dynadot.com/community/help/question/renew-domain
In summary: when signed in, go to My Domains → Manage Domains → click the box beside the domain you want to renew → click Bulk Action and choose Renew → follow thru with the paying process
Additionally, this is a help file about what happens when your domain expires and enters the renewal grace period: https://www.dynadot.com/community/help/question/renewal-grace-period