After upgrading to the 1.5.4 version I can still login to the application.
The dashboard show me all my quotes/invoices correctly.
But when I click on an invoice or quote i get error 503 - Service Unavailable. The server is temporarily busy, try again later!
I can open lists like client overview, invoice overview, etc.
But on every detail I try to open (invoice, quote, client details…), I get the 503 error.