I don’t understand that either. I have been selling on Amazon for nearly 10 years now and they just introduced this Payments Based on Delivery Reserve that applies to everyone, not just new sellers!
How does it make sense to place a 100% hold on an established sellers balance and to keep the funds for weeks after the order’s delivery date?
And it is happening ONLY in Europe. No other Amazon marketplaces are affected. I am 100% sure they wouldn’t be able to get away with it in the USA.
Here you can learn more:
You will need to open a Seller Support case and request that the Payment Based on Delivery Reserve is lifted from your account.
I had it exactly like you and needed to do this to have it lifted.