diff --git a/plugins/fetchinvoice.c b/plugins/fetchinvoice.c
index bf780e23f..8c587d60d 100644
--- a/plugins/fetchinvoice.c
+++ b/plugins/fetchinvoice.c
@@ -643,8 +643,7 @@ static struct pubkey *path_to_node(const tal_t *ctx,
 /* Marshal arguments for sending onion messages */
 struct sending {
 	struct sent *sent;
-	const char *msgfield;
-	const u8 *msgval;
+	struct tlv_onionmsg_payload *payload;
 	struct command_result *(*done)(struct command *cmd,
 				       const char *buf UNUSED,
 				       const jsmntok_t *result UNUSED,
@@ -688,7 +687,7 @@ send_modern_message(struct command *cmd,
 						    &node_alias[i]);
 	}
 	/* Final payload contains the actual data. */
-	payloads[nhops-1] = tlv_onionmsg_payload_new(payloads);
+	payloads[nhops-1] = sending->payload;
 
 	/* We don't include enctlv in final, but it gives us final alias */
 	if (!create_final_enctlv(tmpctx, &blinding_iter, &sent->path[nhops-1],
@@ -700,15 +699,6 @@ send_modern_message(struct command *cmd,
 				    "Could create final enctlv");
 	}
 
-	/* FIXME: This interface is a string for sendobsonionmessage! */
-	if (streq(sending->msgfield, "invoice_request")) {
-		payloads[nhops-1]->invoice_request
-			= cast_const(u8 *, sending->msgval);
-	} else {
-		assert(streq(sending->msgfield, "invoice"));
-		payloads[nhops-1]->invoice
-			= cast_const(u8 *, sending->msgval);
-	}
 	payloads[nhops-1]->reply_path = reply_path;
 
 	req = jsonrpc_request_start(cmd->plugin, cmd, "sendonionmessage",
@@ -783,8 +773,7 @@ static struct command_result *make_reply_path(struct command *cmd,
 
 static struct command_result *send_message(struct command *cmd,
 					   struct sent *sent,
-					   const char *msgfield TAKES,
-					   const u8 *msgval TAKES,
+					   struct tlv_onionmsg_payload *payload STEALS,
 					   struct command_result *(*done)
 					   (struct command *cmd,
 					    const char *buf UNUSED,
@@ -793,8 +782,7 @@ static struct command_result *send_message(struct command *cmd,
 {
 	struct sending *sending = tal(cmd, struct sending);
 	sending->sent = sent;
-	sending->msgfield = tal_strdup(sending, msgfield);
-	sending->msgval = tal_dup_talarr(sending, u8, msgval);
+	sending->payload = tal_steal(sending, payload);
 	sending->done = done;
 
 	return make_reply_path(cmd, sending);
@@ -833,11 +821,12 @@ sendinvreq_after_connect(struct command *cmd,
 			 const jsmntok_t *result UNUSED,
 			 struct sent *sent)
 {
-	u8 *rawinvreq = tal_arr(tmpctx, u8, 0);
-	towire_tlv_invoice_request(&rawinvreq, sent->invreq);
+	struct tlv_onionmsg_payload *payload = tlv_onionmsg_payload_new(sent);
 
-	return send_message(cmd, sent, "invoice_request", rawinvreq,
-			    sendonionmsg_done);
+	payload->invoice_request = tal_arr(payload, u8, 0);
+	towire_tlv_invoice_request(&payload->invoice_request, sent->invreq);
+
+	return send_message(cmd, sent, payload, sendonionmsg_done);
 }
 
 struct connect_attempt {
@@ -1379,9 +1368,12 @@ sendinvoice_after_connect(struct command *cmd,
 			  const jsmntok_t *result UNUSED,
 			  struct sent *sent)
 {
-	u8 *rawinv = tal_arr(tmpctx, u8, 0);
-	towire_tlv_invoice(&rawinv, sent->inv);
-	return send_message(cmd, sent, "invoice", rawinv, prepare_inv_timeout);
+	struct tlv_onionmsg_payload *payload = tlv_onionmsg_payload_new(sent);
+
+	payload->invoice = tal_arr(payload, u8, 0);
+	towire_tlv_invoice(&payload->invoice, sent->inv);
+
+	return send_message(cmd, sent, payload, prepare_inv_timeout);
 }
 
 static struct command_result *createinvoice_done(struct command *cmd,
diff --git a/plugins/offers.c b/plugins/offers.c
index 41a4af4a9..cfe3309cf 100644
--- a/plugins/offers.c
+++ b/plugins/offers.c
@@ -43,12 +43,10 @@ static struct command_result *sendonionmessage_error(struct command *cmd,
 	return command_hook_success(cmd);
 }
 
-/* FIXME: replyfield string interface is to accomodate obsolete API */
 struct command_result *
 send_onion_reply(struct command *cmd,
 		 struct tlv_onionmsg_payload_reply_path *reply_path,
-		 const char *replyfield,
-		 const u8 *replydata)
+		 struct tlv_onionmsg_payload *payload)
 {
 	struct out_req *req;
 	size_t nhops;
@@ -68,18 +66,14 @@ send_onion_reply(struct command *cmd,
 		json_object_start(req->js, NULL);
 		json_add_pubkey(req->js, "id", &reply_path->path[i]->node_id);
 
-		omp = tlv_onionmsg_payload_new(tmpctx);
+		/* Put payload in last hop. */
+		if (i == nhops - 1)
+			omp = payload;
+		else
+			omp = tlv_onionmsg_payload_new(tmpctx);
+
 		omp->encrypted_data_tlv = reply_path->path[i]->encrypted_recipient_data;
 
-		/* Put payload in last hop. */
-		if (i == nhops - 1) {
-			if (streq(replyfield, "invoice")) {
-				omp->invoice = cast_const(u8 *, replydata);
-			} else {
-				assert(streq(replyfield, "invoice_error"));
-				omp->invoice_error = cast_const(u8 *, replydata);
-			}
-		}
 		tlv = tal_arr(tmpctx, u8, 0);
 		towire_tlv_onionmsg_payload(&tlv, omp);
 		json_add_hex_talarr(req->js, "tlv", tlv);
diff --git a/plugins/offers.h b/plugins/offers.h
index ab7a33d80..d283da351 100644
--- a/plugins/offers.h
+++ b/plugins/offers.h
@@ -9,6 +9,5 @@ struct command;
 struct command_result *WARN_UNUSED_RESULT
 send_onion_reply(struct command *cmd,
 		 struct tlv_onionmsg_payload_reply_path *reply_path,
-		 const char *replyfield,
-		 const u8 *replydata);
+		 struct tlv_onionmsg_payload *payload);
 #endif /* LIGHTNING_PLUGINS_OFFERS_H */
diff --git a/plugins/offers_inv_hook.c b/plugins/offers_inv_hook.c
index a2b720f32..680307bee 100644
--- a/plugins/offers_inv_hook.c
+++ b/plugins/offers_inv_hook.c
@@ -26,8 +26,8 @@ fail_inv_level(struct command *cmd,
 	       const char *fmt, va_list ap)
 {
 	char *full_fmt, *msg;
+	struct tlv_onionmsg_payload *payload;
 	struct tlv_invoice_error *err;
-	u8 *errdata;
 
 	full_fmt = tal_fmt(tmpctx, "Failed invoice");
 	if (inv->inv) {
@@ -56,9 +56,10 @@ fail_inv_level(struct command *cmd,
 	err->error = tal_dup_arr(err, char, msg, strlen(msg), 0);
 	/* FIXME: Add suggested_value / erroneous_field! */
 
-	errdata = tal_arr(cmd, u8, 0);
-	towire_tlv_invoice_error(&errdata, err);
-	return send_onion_reply(cmd, inv->reply_path, "invoice_error", errdata);
+	payload = tlv_onionmsg_payload_new(tmpctx);
+	payload->invoice_error = tal_arr(payload, u8, 0);
+	towire_tlv_invoice_error(&payload->invoice_error, err);
+	return send_onion_reply(cmd, inv->reply_path, payload);
 }
 
 static struct command_result *WARN_UNUSED_RESULT
diff --git a/plugins/offers_invreq_hook.c b/plugins/offers_invreq_hook.c
index e8a304fdc..17eb2c688 100644
--- a/plugins/offers_invreq_hook.c
+++ b/plugins/offers_invreq_hook.c
@@ -35,8 +35,8 @@ fail_invreq_level(struct command *cmd,
 		  const char *fmt, va_list ap)
 {
 	char *full_fmt, *msg;
+	struct tlv_onionmsg_payload *payload;
 	struct tlv_invoice_error *err;
-	u8 *errdata;
 
 	full_fmt = tal_fmt(tmpctx, "Failed invoice_request");
 	if (invreq->invreq) {
@@ -61,9 +61,10 @@ fail_invreq_level(struct command *cmd,
 	err->error = tal_dup_arr(err, char, msg, strlen(msg), 0);
 	/* FIXME: Add suggested_value / erroneous_field! */
 
-	errdata = tal_arr(cmd, u8, 0);
-	towire_tlv_invoice_error(&errdata, err);
-	return send_onion_reply(cmd, invreq->reply_path, "invoice_error", errdata);
+	payload = tlv_onionmsg_payload_new(tmpctx);
+	payload->invoice_error = tal_arr(payload, u8, 0);
+	towire_tlv_invoice_error(&payload->invoice_error, err);
+	return send_onion_reply(cmd, invreq->reply_path, payload);
 }
 
 static struct command_result *WARN_UNUSED_RESULT PRINTF_FMT(3,4)
@@ -170,6 +171,7 @@ static struct command_result *createinvoice_done(struct command *cmd,
 {
 	char *hrp;
 	u8 *rawinv;
+	struct tlv_onionmsg_payload *payload;
 	const jsmntok_t *t;
 
 	/* We have a signed invoice, use it as a reply. */
@@ -182,7 +184,9 @@ static struct command_result *createinvoice_done(struct command *cmd,
 					json_tok_full(buf, t));
 	}
 
-	return send_onion_reply(cmd, ir->reply_path, "invoice", rawinv);
+	payload = tlv_onionmsg_payload_new(tmpctx);
+	payload->invoice = rawinv;
+	return send_onion_reply(cmd, ir->reply_path, payload);
 }
 
 static struct command_result *createinvoice_error(struct command *cmd,