Alles original dabei.

no idea, because I would never have needed it, because everything was complete.
You can come and pick up my carrier (unused) if you're interested. Box no longer available.
No defects. LG Francisca Aeschbacher

If I am interpreting the drawings correctly, the adapter I for the F1-3 belts is a short clamping piece through which the belts are pulled and which is then clamped to the inside of the door. This part was included with our version.
To be on the safe side, however, I would ask the manufacturer directly (INTER-UNION Technohandel GmbH, Klaus-von-Klitzing-Straße 2, 76829 Landau - Germany, phone +49 63 41 2 84-0, https://www.inter-union.de.

I had the stand on a Suzuki Swift and it holds up like a dream.

I bought the carrier for a colleague. He fitted it to a Seat without any additional parts.
Good luck.