Difficulties in connecting two projects

I am having trouble connecting two projects, even following the instruction. The idea is to have a first form on which register all demographic data and a second connected one where all necessary documents related to each beneficiary are uploaded. Here the xls files:
Registration for distribution.xlsx (11.5 KB)
Documents for distribution.xlsx (9.9 KB)

Welcome back to the community, @LudovicaUkr! Maybe you will need to play around with the sample attached XLSForm that is available in the support article to learn more on how the syntax links the parent and child project when using the dynamic data attachment feature.