Royalmail Click & Drop stopped connecting

I’m using RM Click & Drop for several years without an issue but tonight the integration disconnected from my Woocommerce store. I couldn’t reconnect it and also deleting it and trying to set it up again from the Click & Drop GUI didn’t help. accotrding to Royailmail there is no issue their end and it must be related to Woocommerce.

The weird thing is that when entering the store URL on C&D normally the standard Woocommerce window asking for permissions to connect pops up (see image below). This doesn’t happen anymore and no RestAPI key is being created in Woocommerce.

What is triggering this Woocommerce popup and what may stop it appearing?