Many exchanges use a shared wallet to track deposits and withdrawals. A memo ID is used to determine which Lumens belong to whom. When withdrawing Lumens from your Stronghold wallet you’ll see an option to add a memo ID.
If the destination service requires a Memo ID, but you haven’t specified it when sending a transaction from Stronghold, your funds will not be credited to your exchange account automatically.
The destination wallet will receive your money, but you will need to let them know, that you forgot to add the Memo ID so they can credit the deposit.
Stronghold is unable to refund your XLM, as the funds have been already transferred from the wallet.
If you forgot to specify the Memo when making a transaction, or provided the incorrect Memo ID, please contact the receiver service and provide them with the transaction ID, details and correct Memo ID.