Is it possible to select the Point Relais before payment ?
Hey, sadly this is not possible...
We're really sorry but 'cause of security limitation in Shopify Checkout process this is impossible to select the Points Relais aka Pick Up And Go locations before payment, except if you're using Shopify Plus Plan.
We hope the technical Shopify team we'll soon allow us to add this feature before payment. We'll keep you up to date :-)