There are a number of different errors that the Quality check will show. One of the errors you can encounter has the format 'availability'/'condition'/'mpn' is not connected to a field, check the mapping in 'Finalize'.
When you see this error it means that in the Finalize-step you have not linked an internal field to the channel field name. Clicking on the error will forward you to the Finalize-step where you will see a "-" symbol under the internal field.
To solve the error you need to link an internal field to the channel field name in the Finalize-step. For example, for the channel field name "availability" you can link the internal field "availability".