There are a number of reasons for this problem. The most common are that the incorrect payee/collateral/reward address is being used.
Another possibility is that the MN is on the wrong chain, and so is not showing on the correct one and hence we don't see it. Or in some cases it could be that we are on the wrong chain and thus don't see your node (a rarity but can happen due to forks because of chain issues, or lack of wallet updates to reduce forks from happening). These forks can either affect the MN owner, as well as even us, so it's something out of our control.
Anyway, back to the first type. The majority of chains utilise the collateral address for adding nodes. However, there are some chains that try to simplify this procedure by utilising a different address. For example, Stakecube (SCC) we have had a number of users recently mentioning that they cannot add their nodes. Now this seems to be because SCC are now doing things a little differently. With SCC you need to use what they call the "rewards" address. So once you then use the correct address, you can add your SCC nodes without issues.
Irrespective if this is SCC or other coins, we will show you below how you can check/verify if you are using the correct payee/collateral/rewards address to add to our system for monitoring purposes. Within your wallet, or on the masternode you can issue commands such as masternode list full or masternode list (depending on the codebase, eg: Dash/Pivx). These are the commands that you are going to use to find your node. This will be easier on the masternode itself since we can use standard Linux commands to filter the list.
Here I am going to use SCC as an example, but the same procedure applies to any chain with masternodes. You will need your TXID for that masternode, maybe even the IP address of your masternode if you prefer to filter by this to try and find the correct payee.
First we are going to filter by payee. If you get a result, then this means you have the correct payee/collateral/reward address and can add to your system. If you don't then we need to continue with other commands.
scc-cli masternode list full sLB123451Xr1LWn5C5N6Wof1TrC3pfz9vP
"12345b9ecc0f3199c40fabc944c69dc6e1e84291e872be495ec5420c3969e12345-0": " ENABLED sLB312345Xr1LWn5C5N6Wof1TrC3pfz9vP 0 0 [1234:abcd:9876:2222::4]:40000"
the above is an example using a random MN from the masternode list. However, assuming I did put the correct payee address, I found my node and can add it using that payee address. If there were no results, then I need to try and find it by using the TXID or IP address if the chain actually displays it (not all chains do). So now, we are going to assume I didn't find my node, so now we will use the TXID to find our node.
scc-cli masternode list full 12345b9ecc0f3199c40fabc944c69dc6e1e84291e872be495ec5420c3969e12345-0
"12345b9ecc0f3199c40fabc944c69dc6e1e84291e872be495ec5420c3969e12345-0": " ENABLED sLB123451Xr1LWn5C5N6Wof1TrC3pfz9vP 0 0 [1234:abcd:9876:2222::4]:40000"
using the TXID is most likely always going to work, since if you are unsure of the payee, then it's best just to filter by TXID, and you are guaranteed to find it the first time. So now I got my result, I see the payee address and this is the one I use to add it to NodeCheck for MN monitoring.
The other issue, relating to checking if your node is forked or not, you can find that in our article: What the fork?