Yes, in order to add a Tumblr feed onto your website, you will need to use a third party app. Here is a free and is easy to setup app - https://www.powr.io/tutorials/how-to-add-tumblr-feed-plugin-to-your-weebly-site
Note: These apps are created by third-party developers and act as extensions to the Weebly platform. For this reason, we do not offer support for these third-party applications. If you need assistance with these apps, you will want to reach out to the app developers directly. Some apps also have an additional cost associated with them. This cost is not included in your Flipcause subscription and will be paid directly to the developers.