common: coin movements for payments need group id as well as part id.

diff --git a/common/coin_mvt.c b/common/coin_mvt.c
index d0d6d500..d1f97322 100644
--- a/common/coin_mvt.c
+++ b/common/coin_mvt.c
@@ -51,7 +51,8 @@ enum mvt_tag *new_tag_arr(const tal_t *ctx, enum mvt_tag tag)
 struct channel_coin_mvt *new_channel_coin_mvt(const tal_t *ctx,
 					      const struct channel_id *cid,
 					      const struct sha256 *payment_hash TAKES,
-					      const u64 *part_id TAKES,
+					      const u64 *part_id,
+					      const u64 *group_id,
 					      struct amount_msat amount,
 					      const enum mvt_tag *tags TAKES,
 					      bool is_credit,
@@ -61,7 +62,15 @@ struct channel_coin_mvt *new_channel_coin_mvt(const tal_t *ctx,
 
 	mvt->chan_id = *cid;
 	mvt->payment_hash = tal_dup_or_null(mvt, struct sha256, payment_hash);
-	mvt->part_id = tal_dup_or_null(mvt, u64, part_id);
+	if (!part_id) {
+		assert(!group_id);
+		mvt->part_and_group = NULL;
+	} else {
+		mvt->part_and_group = tal(mvt, struct channel_coin_mvt_id);
+		mvt->part_and_group->part_id = *part_id;
+		mvt->part_and_group->group_id = *group_id;
+	}
+
 	mvt->tags = tal_dup_talarr(mvt, enum mvt_tag, tags);
 
 	if (is_credit) {
@@ -380,7 +389,7 @@ struct channel_coin_mvt *new_coin_channel_push(const tal_t *ctx,
 					       bool is_credit)
 {
 	return new_channel_coin_mvt(ctx, cid, NULL,
-				    NULL, amount,
+				    NULL, NULL, amount,
 				    take(new_tag_arr(NULL, tag)), is_credit,
 				    AMOUNT_MSAT(0));
 }
diff --git a/common/coin_mvt.h b/common/coin_mvt.h
index 664b3ac9..474a9678 100644
--- a/common/coin_mvt.h
+++ b/common/coin_mvt.h
@@ -37,6 +37,13 @@ enum mvt_tag {
 	SPLICE = 23,
 };
 
+struct channel_coin_mvt_id {
+	/* multi-part payments may share a payment hash,
+	 * so we should also record part-id and group-id for them */
+	u64 part_id;
+	u64 group_id;
+};
+
 struct channel_coin_mvt {
 	/* account_id */
 	struct channel_id chan_id;
@@ -44,9 +51,9 @@ struct channel_coin_mvt {
 	/* identifier */
 	struct sha256 *payment_hash;
 
-	/* mutli-part payments may share a payment hash,
-	 * so we should also record a 'part-id' for them */
-	u64 *part_id;
+	/* multi-part payments may share a payment hash,
+	 * so we should also record part-id and group-id for them */
+	struct channel_coin_mvt_id *part_and_group;
 
 	/* label / tag array */
 	enum mvt_tag *tags;
@@ -96,10 +103,12 @@ struct chain_coin_mvt {
 
 enum mvt_tag *new_tag_arr(const tal_t *ctx, enum mvt_tag tag);
 
+/* Either part_id and group_id both NULL, or neither are */
 struct channel_coin_mvt *new_channel_coin_mvt(const tal_t *ctx,
 					      const struct channel_id *cid,
 					      const struct sha256 *payment_hash TAKES,
-					      const u64 *part_id TAKES,
+					      const u64 *part_id,
+					      const u64 *group_id,
 					      struct amount_msat amount,
 					      const enum mvt_tag *tags TAKES,
 					      bool is_credit,
diff --git a/doc/developers-guide/plugin-development/event-notifications.md b/doc/developers-guide/plugin-development/event-notifications.md
index bc649c98..37d69a77 100644
--- a/doc/developers-guide/plugin-development/event-notifications.md
+++ b/doc/developers-guide/plugin-development/event-notifications.md
@@ -333,6 +333,7 @@ A notification for topic `coin_movement` is sent to record the movement of coins
 		"vout":1, // (`chain_mvt` only)
 		"payment_hash": "xxx", // (either type, optional on both)
 		"part_id": 0, // (`channel_mvt` only, optional)
+		"group_id": 0, // (`channel_mvt` only, optional)
 		"credit_msat":2000000000,
 		"debit_msat":0,
 		"output_msat": 2000000000, // ('chain_mvt' only)
@@ -364,7 +365,7 @@ _Only_ tagged on external events (deposits/withdrawals to an external party).
 
 `payment_hash` is the hash of the preimage used to move this payment. Only present for HTLC mediated moves (both `chain_mvt` and `channel_mvt`) A `chain_mvt` will have a `payment_hash` iff it's recording an htlc that was fulfilled onchain.
 
-`part_id` is an identifier for parts of a multi-part payment. useful for aggregating payments for an invoice or to indicate why a payment hash appears multiple times. `channel_mvt` only
+`part_id` and `group_id` are identifiers for parts of a multi-part payment. useful for aggregating payments for an invoice or to indicate why a payment hash appears multiple times. `channel_mvt` only
 
 `credit` and `debit` are millisatoshi denominated amounts of the fund movement. A  
 'credit' is funds deposited into an account; a `debit` is funds withdrawn.
diff --git a/lightningd/coin_mvts.c b/lightningd/coin_mvts.c
index 5ac2ef98..80cd0b22 100644
--- a/lightningd/coin_mvts.c
+++ b/lightningd/coin_mvts.c
@@ -11,7 +11,7 @@ struct channel_coin_mvt *new_channel_mvt_invoice_hin(const tal_t *ctx,
 						     const struct channel *channel)
 {
 	return new_channel_coin_mvt(ctx, &channel->cid,
-				    &hin->payment_hash, NULL,
+				    &hin->payment_hash, NULL, NULL,
 				    hin->msat, new_tag_arr(ctx, INVOICE),
 				    true, AMOUNT_MSAT(0));
 }
@@ -30,7 +30,7 @@ struct channel_coin_mvt *new_channel_mvt_routed_hin(const tal_t *ctx,
 		return NULL;
 
 	return new_channel_coin_mvt(ctx, &channel->cid,
-				    &hin->payment_hash, NULL,
+				    &hin->payment_hash, NULL, NULL,
 				    hin->msat, new_tag_arr(ctx, ROUTED),
 				    true, fees_collected);
 }
@@ -40,7 +40,9 @@ struct channel_coin_mvt *new_channel_mvt_invoice_hout(const tal_t *ctx,
 						      const struct channel *channel)
 {
 	return new_channel_coin_mvt(ctx, &channel->cid,
-				    &hout->payment_hash, &hout->partid,
+				    &hout->payment_hash,
+				    &hout->partid,
+				    &hout->groupid,
 				    hout->msat, new_tag_arr(ctx, INVOICE),
 				    false, hout->fees);
 }
@@ -50,7 +52,7 @@ struct channel_coin_mvt *new_channel_mvt_routed_hout(const tal_t *ctx,
 						     const struct channel *channel)
 {
 	return new_channel_coin_mvt(ctx, &channel->cid,
-				    &hout->payment_hash, NULL,
+				    &hout->payment_hash, NULL, NULL,
 				    hout->msat, new_tag_arr(ctx, ROUTED),
 				    false,
 				    hout->fees);
diff --git a/lightningd/notification.c b/lightningd/notification.c
index cb60dabd..6368ec27 100644
--- a/lightningd/notification.c
+++ b/lightningd/notification.c
@@ -505,8 +505,10 @@ static void channel_movement_notification_serialize(struct json_stream *stream,
 	/* push funding / leases don't have a payment_hash */
 	if (chan_mvt->payment_hash)
 		json_add_sha256(stream, "payment_hash", chan_mvt->payment_hash);
-	if (chan_mvt->part_id)
-		json_add_u64(stream, "part_id", *chan_mvt->part_id);
+	if (chan_mvt->part_and_group) {
+		json_add_u64(stream, "part_id", chan_mvt->part_and_group->part_id);
+		json_add_u64(stream, "group_id", chan_mvt->part_and_group->group_id);
+	}
 	json_add_amount_msat(stream, "credit_msat", chan_mvt->credit);
 	json_add_amount_msat(stream, "debit_msat", chan_mvt->debit);
 	json_add_amount_msat(stream, "fees_msat", chan_mvt->fees);