Hello Samantha
Even if they are the same brand, this adapter is there so that the pram and the infant carrier have a connection.
In the description you can see which prams from ABC and which infant carriers can be connected with this adapter.
Otherwise, you can also go to the ABC website and look under accessories to see which pram and which baby seat you have, then you will see which adapter you need.

Hi Samantha
Maxi Cosi is a brand that produces child seats. So you probably just have a child seat from Abc design and I assume that they are compatible with the pram. But it's best to try them out and otherwise Galaxus has very fast delivery times. We need our adapters (Maxi Cosi --> Abc design) no more than once a month.
LG Bernhard