The payment screen shows the way back in
If your account session expires while you are paying, the payment screen itself offers the button to sign back in.
A maintenance update to the licence payment. You pay for it through your JUDLEX account, and that account closes its session on its own once it has gone a while untouched. The payment screen, on the other hand, is one of those that stay open: you open it, the phone rings, and you come back to it a good while later.
An expired session comes with its own way in
When that happens, the payment screen says so and offers you the button to sign back into your account right there. You sign in and carry on paying from where you left off.