Hey, it’s working now…
The only two changes was:
C:\Windows\System32\inetsrv\appcmd.exe set config "My WebSite" /section:requestfiltering /requestlimits.maxallowedcontentlength:4294967295"
Default: 30000000
C:\Windows\System32\inetsrv\appcmd.exe set config "My WebSite" /section:system.web/httpRuntime /maxRequestLength:512000
Default: 4096
Here was the connection test:
2019-12-11 15:30:12 W3SVC31 www 10.0.1.30 PROPFIND /test/ - 443 WWW\wd.bucher-allround 12-34-56-78.dynamic.hispeed.ch HTTP/1.1 Duplicati+WEBDAV+Client+v2.0.4.23 - - www.bucher-allround.ch 207 0 0 1157 776 15
Here the backup itself:
2019-12-11 15:33:29 W3SVC31 www 10.0.1.30 PROPFIND /test/ - 443 WWW\wd.bucher-allround 12-34-45-67.dynamic.hispeed.ch HTTP/1.1 Duplicati+WEBDAV+Client+v2.0.4.23 - - www.bucher-allround.ch 207 0 0 1157 776 15
2019-12-11 15:33:29 W3SVC31 www 10.0.1.30 PUT /test/duplicati-b1177fc17aafc4338881f769cee78d8de.dblock.zip - 443 WWW\wd.bucher-allround 12-34-45-67.dynamic.hispeed.ch HTTP/1.1 Duplicati+WEBDAV+Client+v2.0.4.23 - - www.bucher-allround.ch 201 0 0 320 1353 31
2019-12-11 15:33:29 W3SVC31 www 10.0.1.30 PUT /test/duplicati-id39bd712b35643ff99294ed5334a5394.dindex.zip - 443 WWW\wd.bucher-allround 12-34-45-67.dynamic.hispeed.ch HTTP/1.1 Duplicati+WEBDAV+Client+v2.0.4.23 - - www.bucher-allround.ch 201 0 0 320 1422 46
2019-12-11 15:33:29 W3SVC31 www 10.0.1.30 PUT /test/duplicati-20191211T153328Z.dlist.zip - 443 WWW\wd.bucher-allround 12-34-45-67.dynamic.hispeed.ch HTTP/1.1 Duplicati+WEBDAV+Client+v2.0.4.23 - - www.bucher-allround.ch 201 0 0 320 1309 31
2019-12-11 15:33:29 W3SVC31 www 10.0.1.30 PROPFIND /test/ - 443 WWW\wd.bucher-allround 12-34-45-67.dynamic.hispeed.ch HTTP/1.1 Duplicati+WEBDAV+Client+v2.0.4.23 - - www.bucher-allround.ch 207 0 0 3909 776 31
2019-12-11 15:33:29 W3SVC31 www 10.0.1.30 GET /test/duplicati-20191211T153328Z.dlist.zip - 443 WWW\wd.bucher-allround 12-34-45-67.dynamic.hispeed.ch HTTP/1.1 Duplicati+WEBDAV+Client+v2.0.4.23 - - www.bucher-allround.ch 200 0 0 905 754 15
2019-12-11 15:33:29 W3SVC31 www 10.0.1.30 GET /test/duplicati-id39bd712b35643ff99294ed5334a5394.dindex.zip - 443 WWW\wd.bucher-allround 12-34-45-67.dynamic.hispeed.ch HTTP/1.1 Duplicati+WEBDAV+Client+v2.0.4.23 - - www.bucher-allround.ch 200 0 0 1000 772 15
2019-12-11 15:33:29 W3SVC31 www 10.0.1.30 GET /test/duplicati-b1177fc17aafc4338881f769cee78d8de.dblock.zip - 443 WWW\wd.bucher-allround 12-34-45-67.dynamic.hispeed.ch HTTP/1.1 Duplicati+WEBDAV+Client+v2.0.4.23 - - www.bucher-allround.ch 200 0 0 931 772 15
2019-12-11 15:34:37 W3SVC31 www 10.0.1.30 PROPFIND /test/ - 443 WWW\wd.bucher-allround 12-34-45-67.dynamic.hispeed.ch HTTP/1.1 Duplicati+WEBDAV+Client+v2.0.4.23 - - www.bucher-allround.ch 207 0 0 3903 776 35
2019-12-11 15:34:51 W3SVC31 www 10.0.1.30 PUT /test/duplicati-b35ed11e201f1430da14f156f03342bf7.dblock.zip - 443 WWW\wd.bucher-allround 12-34-45-67.dynamic.hispeed.ch HTTP/1.1 Duplicati+WEBDAV+Client+v2.0.4.23 - - www.bucher-allround.ch 201 0 0 320 21791828 8345
2019-12-11 15:34:51 W3SVC31 www 10.0.1.30 PUT /test/duplicati-id2ddc32417ba4244994bc7bbee13de6b.dindex.zip - 443 WWW\wd.bucher-allround 12-34-45-67.dynamic.hispeed.ch HTTP/1.1 Duplicati+WEBDAV+Client+v2.0.4.23 - - www.bucher-allround.ch 201 0 0 320 165845 109
2019-12-11 15:34:51 W3SVC31 www 10.0.1.30 PUT /test/duplicati-20191211T153436Z.dlist.zip - 443 WWW\wd.bucher-allround 12-34-45-67.dynamic.hispeed.ch HTTP/1.1 Duplicati+WEBDAV+Client+v2.0.4.23 - - www.bucher-allround.ch 201 0 0 320 186677 203
2019-12-11 15:34:51 W3SVC31 www 10.0.1.30 PROPFIND /test/ - 443 WWW\wd.bucher-allround 12-34-45-67.dynamic.hispeed.ch HTTP/1.1 Duplicati+WEBDAV+Client+v2.0.4.23 - - www.bucher-allround.ch 207 0 0 6663 776 15
2019-12-11 15:34:51 W3SVC31 www 10.0.1.30 GET /test/duplicati-20191211T153436Z.dlist.zip - 443 WWW\wd.bucher-allround 12-34-45-67.dynamic.hispeed.ch HTTP/1.1 Duplicati+WEBDAV+Client+v2.0.4.23 - - www.bucher-allround.ch 200 0 0 186591 754 78
2019-12-11 15:34:51 W3SVC31 www 10.0.1.30 GET /test/duplicati-id2ddc32417ba4244994bc7bbee13de6b.dindex.zip - 443 WWW\wd.bucher-allround 12-34-45-67.dynamic.hispeed.ch HTTP/1.1 Duplicati+WEBDAV+Client+v2.0.4.23 - - www.bucher-allround.ch 200 0 0 165713 772 93
2019-12-11 15:34:55 W3SVC31 www 10.0.1.30 GET /test/duplicati-b35ed11e201f1430da14f156f03342bf7.dblock.zip - 443 WWW\wd.bucher-allround 12-34-45-67.dynamic.hispeed.ch HTTP/1.1 Duplicati+WEBDAV+Client+v2.0.4.23 - - www.bucher-allround.ch 200 0 0 21829976 772 2937
I will repeat the same steps on another client again. Let you know the outcome.