You need to follow these steps for each shop you wish to connect:
Create New Shopware 6 Connection
Go to the Adribute app.
Navigate to "Connections".
Click on "Create Connection" in the top right corner.
Search for the Shopware 6 connection and select it.
Fill in your Shopware URL, which simply is your Store URL, e.g. https://adtribute.shop.com/
If your store is not hosted by your customer-facing URL, please use the URL which your domain is hosted on. You can find your domains here: "Settings" > "System" > "Domains", then use the according domain.
Now you need your Client ID and Client Secret from Shopware.
Retrieve Client ID and Client Secret from Shopware
Open Shopware.
Navigate to "Settings" > "System" > "Integrations".
Click "Create integration" at the top right.
Name the integration "adtribute"
Select a Role with Permissions that grant view access to the following (to create a new role, read this Shopware help article):
Oders
Products
Retrieve Client ID
Copy the "Access key ID" by clicking on the clipboard icon.
Paste the ID into the "Client ID" field in adtribute.
Retrieve Client Secret
Copy the "Secret access key" by clicking on the clipboard icon.
Paste the ID into the "Client Secret" field in adtribute.
Once you have pasted both the ID and Secret into adtribute, click on "Save integration" on to bottom right in Shopware.
Complete Connection
After you have pasted the Client ID and the Client Secret and saved the Integration in Shopware, just click on "Next". It will load for a short bit and tell you on the bottom right if the Connection was successful and show up within your Connections.
You have to repeat those steps for every Shopware store, you wish to connect.