memo
The memo ID extracted from the sub claim.
SEP-10 supports memo IDs in the subject claim using the format "ACCOUNT:MEMO". This is commonly used by wallet applications to associate tokens with specific sub-accounts or sessions.
Example:
sub = "GACCOUNT..."→memo = nullsub = "GACCOUNT...:12345"→memo = "12345"
Return
The memo string, or null if no memo is present in the subject