When you create a Stellar Lumens (XLM) deposit address under your Kraken account, a unique ‘Memo’ is also generated. This Memo is an extra piece of information that can be included when sending a Lumens transaction.
On Kraken, the Memo is used to determine what account a given transaction should be assigned and credited to. This is because all Kraken accounts use a single Lumens deposit address
The Memo is numerical and has to be included with all XLM deposits to your Kraken account. An example Memo is:
Always ensure to include the correct Memo before sending your XLM deposit. Leaving out this information will lead to significant delays in crediting the transaction to your account, and can be irretrievable in certain cases.
If you forgot to include the memo submit a support ticket here.