Can't connect to NAS with iOS 13.1 Files app

I have iOS 13.1 on my iPhone and iPadOS 13.1 on my iPad Pro. I'm trying to use the Files app's new Connect to Server feature to connect to my Synology NAS DS213 box. But I keep getting an error message that it can't connect to the server. This happens both on the iPhone and iPad. I've enabled SMB on the NAS. I know it works because I can connect to the NAS from my two Macs and my Windows computer using SMB. On my iPhone and iPad, I've tried connecting using all the different permutations for the NAS - by name, by IP address, including the smb://, not including smb://. putting .local at the end of the host name, not putting .local at the end. Nothing works. Just keep getting a generic error that it can't connect to the server. Has anyone else tried connecting to a Synology NAS or other brand NAS with the new Files app? Working? Not working? Appreciate any feedback and troubleshooting help you can offer. Thank you.