In order to connect a Salesforce marketing cloud data source you need to install our app within your salesforce organization. You can find the install url here or in the connect dialogue. Currently you need to be logged in to the marketing cloud in the same browser session (as in another tab) before trying to install the app. Otherwise the install url will prompt you to log in which might fail for some setups.

To create and install packages you must have the Installed Package | Administer permission. This permission is automatically applied to the Administrator and Marketing Cloud Administrator system-defined roles. Add the permission for a different role or user in the Administration area in order for this to work.

More about this can be found on the official Marketing Cloud documentation.

After the app has been installed, please make sure that the user connecting has access to it within Salesforce. This can be done under Setup>Apps>Installed Packages>Funnel Marketing Cloud Package v2>Access. Notice that this will need to be done for each business unit.

Keep in mind that when you install the app, and/or change the access rights, it might take a couple of minutes until the changes actually go through.

Example of what it looks like here: