diff --git a/packages/core/src/errors/codes.ts b/packages/core/src/errors/codes.ts
index 1545868..c7615f1 100644
--- a/packages/core/src/errors/codes.ts
+++ b/packages/core/src/errors/codes.ts
@@ -50,6 +50,10 @@ export const STELLAR_ERROR_CODES = {
   // ── Validation ─────────────────────────────────────────────────────────
   /** Caller-supplied input was invalid or the environment was unsupported. */
   VALIDATION_ERROR: "VALIDATION_ERROR",
+  /** The supplied memo is invalid for its type (too long, wrong format, etc.). */
+  INVALID_MEMO: "INVALID_MEMO",
+  /** The destination requires a memo (SEP-29) but none was supplied. */
+  MEMO_REQUIRED: "MEMO_REQUIRED",
 
   // ── Network ────────────────────────────────────────────────────────────
   /** A transport-level failure (offline, DNS, timeout, CORS, etc.). */
@@ -94,6 +98,8 @@ export const DEFAULT_ERROR_MESSAGES: Record<StellarErrorCode, string> = {
     "The requested start ledger is older than this RPC server retains. Use a more recent ledger, or an archival RPC provider.",
   RATE_LIMITED: "Too many requests were sent to Horizon. Please slow down and try again.",
   VALIDATION_ERROR: "The provided input is invalid.",
+  INVALID_MEMO: "The memo is invalid. Check the memo type and its length/format.",
+  MEMO_REQUIRED: "The destination account requires a memo. Add one before sending.",
   NETWORK_ERROR: "Unable to reach the Stellar network. Check your connection and try again.",
   UNKNOWN: "An unknown error occurred.",
 o  SEP10_VALIDATION_FAILED: "The SEP-10 authentication challenge failed validation. It may be malformed or tampered with.",
diff --git a/packages/core/src/types/index.ts b/packages/core/src/types/index.ts
index 1b26a3b..ee9f932 100644
--- a/packages/core/src/types/index.ts
+++ b/packages/core/src/types/index.ts
@@ -356,6 +356,49 @@ export interface TransactionResult {
   envelope?: string
 }
 
+/**
+ * Fee controls shared by every hook that builds a Horizon transaction.
+ *
+ * Stellar prices transactions by auction: each ledger has limited capacity,
+ * and when more transactions are submitted than fit, the network takes the
+ * highest bidders and rejects the rest with `tx_insufficient_fee`.
+ *
+ * **A fee is a maximum bid, not a charge.** The network only ever takes what
+ * it needs to include your transaction, so bidding generously costs nothing in
+ * the common case and is what keeps a transaction landing during congestion.
+ */
+export interface FeeOptions {
+  /**
+   * Explicit fee in stroops, per operation. Wins over everything else.
+   *
+   * @example
+   * send({ to, asset: "XLM", amount: "10", fee: "10000" })
+   */
+  fee?: string
+  /**
+   * Multiplier applied to the network's current base fee, fetched from
+   * Horizon at build time. Defaults to {@link DEFAULT_FEE_MULTIPLIER}.
+   *
+   * @example
+   * send({ to, asset: "XLM", amount: "10", feeMultiplier: 10 })
+   */
+  feeMultiplier?: number
+}
+
+/**
+ * A memo to attach to a payment. A bare string is treated as `MEMO_TEXT`.
+ *
+ * - `text`: <= 28 UTF-8 bytes
+ * - `id`: unsigned 64-bit integer as a string; do not parse it to a JavaScript `number`
+ * - `hash` / `return`: exactly 64 hexadecimal characters (32 bytes)
+ */
+export type MemoInput =
+  | string
+  | { type: "text"; value: string }
+  | { type: "id"; value: string }
+  | { type: "hash"; value: string }
+  | { type: "return"; value: string }
+
 /**
  * Options for sending a payment transaction.
  */
@@ -363,7 +406,7 @@ export interface SendPaymentOptions {
   to: string
   asset: Asset
   amount: string
-  memo?: string
+  memo?: MemoInput
 }
 
 /**