Attribute as Key Figure

Hello Experts,

I am currently having some issue with Attribute as Key Figure. I tried to create one, following this procedure :

1. Attribute creation (with decimal data type), and assignment to relevant Master Data Type.

2. Attribute assignment to the planning area (with Key Figure checkbox).

3. Key figure configuration, as shown below.

4. Master Data import job via CSV file.

From your experience, is there anything particular that I might have forgotten? I keep on getting this error message in Excel when I try to open a planning view on this KF :

Thanks for your help.

Regards.