Check if your account has analytical/cost axis enabled.
For that, log into your Exact Online account, select the "Financial" tab and "analysis & Results" (In the case of the account in the image below, there are two axis. Both cost centres and cost units are enabled).

Step 1: Choose a name for your connexion.

Step 2: Define the analytical/cost axis to activate.

Step 3: Click "Authorise" to finalise the connexion

You will be redirected to an Exact Online page to authenticate your account

Step 1: Select the company, folder, division you like to configure.

ATTENTION: it is possible that you don't find the company/division you want to connect in the dropdown menu. If this is the case, you need to adapt the allowed companies/divisions through the Exact Online interface:
1) Open Exact Online "Import/Export" Settings

2) Select "App permissions"

3) Select the app you are trying to connect to Exact Online

4) Go to the "Permitted companies" section. Here you can allow all current and future companies OR select "Manage companies" to only allow specific companies

Step 2: Click "Submit" to finalise the configuration.
