Really struggling with GeoTracking and OneLink – help please.

Hi everyone, I am getting really confused with my Amazon Affiliate links, OneLink and Geotracking and hoping someone can help me.
Essentially I am based in the UK as a therapist. I have amazon affiliate links set up for books I recommend. Originally these links were generated through my Amazon UK affiliate links. I then had a look through my analytics and realised most of traffic actually comes from the USA meaning I was likely missing out on commission.
I had a look around at what I could do and I found this idea of OneLink, which appeared to take into consideration geo tracking.
I subsequently set up a US Amazon affiliate account, and then linked the stores. If I log into the my Amazon UK affiliate account I can see the linked stores are linked, if I log into my US Amazon affiliate account I can see that the same accounts are linked, so that looks like it is set up correctly.
I thought I would test it out. I generated a UK amazon affiliate link for a book. I then turned on my VPN and set it to USA, and clicked on my generated link. It still loads that link in UK Amazon store and does not redirect to the US Amazon as I think it should. Like wise, if I generate a US Amazon link, and then click on it in the UK it takes me to Amazon.com and not the UK amazon site, so none of this seems like its working properly. What am I doing wrong? For the time being I am running different links for different countries but this has ended up in my producing 4 links for every book – 1 for US Amazon, 1 for UK Amazon and then Kindle / physical books for both of those.
I have also set up amazon influencer accounts for each country – but that doesnt seem to help me as it doesnt seem to offer geo tracking at all.
How do I move forward with this?
Thanks for any help.