I setup OpenDNS successfully on OpenWRT. However I have problem getting OpenWRT to update my IP address on OpenDNS.
Under the DDNS configuration section I selected OpenDNS as service provider and entered my username and password for OpenDNS, however there is a Lookup Hostname and Domain section that I am unsure what to fill in with.
You need to register with some DDNS-provider and you will get the required parameters: https://openwrt.org/docs/guide-user/services/ddns/client
Sign in to the DDNS-provider site, navigate to your profile and search for your hostname/domain there.
I read that; and even after you clarified again, I still have no clue how DNS-O-Matic nor how OpenDNS are involved here. It seems you use them to update all DDNS, instead of just configuring them in OpenWrt.
Perhaps you need the manual from DNS-O-Matic???
Use custom DDNS client.
Nonetheless, on your picture from DNS-O-Matic, we see:
Users need to enter a DNS-O-Matic username and password. DNS-O-Matic usernames are 3-25 characters. DNS-O-Matic passwords are 6-20 characters. All ASCII letters and numbers accepted. Dots, dashes, and underscores allowed, but not at the beginning or end of the string.
Users will also enter a list of hostnames (FQDNs) to be updated.
Hostname you wish to update. To update all services registered with DNS-O-Matic to the new IP address, hostname may be omitted or set to all.dnsomatic.com (useful if required by client). This field is also used for services that use different names for the unique identifier of the target being updated (ex. freedns.afraid.org, TZO). DNS-O-Matic will format the update string appropriately for each supported service at distribution.
So to fix your issue (adhering to the 2015 Wiki), make an instance for BOTH domains - OR LEAVE THE DOMAIN AS UPDATES AND OMIT THE HOSTNAME PARAMETER
Set Custom update-url to http://[USERNAME]:[PASSWORD]@updates.dnsomatic.com/nic/update?hostname=all.dnsomatic.com&myip=[IP]&wildcard=NOCHG&mx=NOCHG&backmx=NOCHG
Perhaps just easier to read...but the all.dnsomatic.com domain...you must have forgot that you told me: