As part of a pilot action, if the whole costs fall under the category of external costs, but it is linked to concrete measures on a pilot area, do we need to fill out the section “Investment”?

The necessity to fill the investment section in the Application Form depends on the output of the external service you will use. If the result becomes an asset of your organisation (e.g. a digital tool) it is considered as investment and the corresponding section should be filled in the Application Form.