Foscam has discontinued their DDNS service as of December 31st 2020 so if you are/were using this service you'll have to find an alternate. Please see this article for more information:
Where possible we recommend switching to P2P remote access if it is supported in your devices.
If you are using another DDNS provider or direct IP connection, you will want to confirm that the DDNS address is getting updated if/when your home's external (WAN) IP changes. Also please confirm the port is properly forwarded and can be seen remotely. Some internet providers may block port forwarding. In some cases port forwarding isn't available such as on some shared cellular type Internet plans.
Please read this Foscam help article on direct / DDNS remote access and port forwarding: