Cant login to existing amazon account to integrate with shopify

[PG74]

I am trying to go through the integration process enabling Amazon Pay on my Shopify store. Should be straightforward enough.

I have an existing Amazon seller account - when going through the first steps of the process, it is defaulting to add a new amazon account... I cant for the life of me find a way to log in to my existing account. It can only start a new one.

I thought it was a cookies issue, tried multiple browsers, and the same thing is happening.

Any thoughts?