Hi @DanSir, welcome to the forum!
It sounds like you previously were getting successful Duplicati backups to Sia until they updated to 1.3.4, is that correct?
Not that it likely matters, but what version of Duplicati are you using, on what OS, and are you doing anything crazy like @TitaniumCoder477 (Sia backup gateway appliance)?
If you’re just using it as a standard destination, hopefully another Sia user such as @drakar2007 or @evlvd (Sia 1.3.6 API Password Integration) might have some thoughts.