Please perform the following steps to resolve the issue:
1- Check the strength of internet connection (mobile data or Wi-Fi), it should be strong.
2- Clear the data from Download manger (Settings > Apps > tap on 3 dots > show system apps > Download manager > storage > clear data).
For further assistance, register your concern in Samsung members app (Open Samsung members app > click on “+“icon > send feedback > Error report/Ask Questions).
Team Samsung Members