What do I need to know?

When registering a Google Ads account, matelso asks for the rights of an administrative account in your Google Ads account. Here, matelso does not ask for owner rights.
In an infomail to its customers in June 2020, Google describes the step that only exactly one (1) administrative account can still have ownership. This right is not requested and not required for a functioning integration of Google Ads in matelso.
They should therefore see a "No" in the Owner column in the row that says "matelso Call Tracking AdWordManager" in their management accounts view.

Management accounts can only be managed by one (1) management account. This means that the matelso Ads Integration cannot transfer data to a managed administrative account. This restriction does not apply to Ads accounts themselves but only to management accounts.

An Ads management account structure may be a maximum of 5 levels deep. Once these 5 levels are reached, no management account can be switched via the structure and the Ads integration must be directly linked to the Ads accounts.