Are you able to share a screenshot of the field details? It should be editable if you created the field as Marketo only. Also, if the field name is LookBook Company, is that the field you are selecting for attribute in the flow action?
and
Does this shed some light?
Yes, it looks like the issue is with the field type. I found definitions in the discussion below that explains "Float" is for numbers with decimals so that is likely why the token is invalid. I generally use field type "String" for my text fields.
it never should have been a float -- definitely should be a string.
This solved the problem. Many thanks Emily Dick and thanks too Josh Hill 🙂