diff --git a/alphabet/alphabet.tpl b/alphabet/alphabet.tpl
index 27f6b67..39a2360 100644
--- a/alphabet/alphabet.tpl
+++ b/alphabet/alphabet.tpl
@@ -1,6 +1,7 @@
 package alphabetcontract
 
 import (
+	"github.com/nspcc-dev/neo-go/pkg/interop"
 	"github.com/nspcc-dev/neo-go/pkg/interop/binary"
 	"github.com/nspcc-dev/neo-go/pkg/interop/contract"
 	"github.com/nspcc-dev/neo-go/pkg/interop/crypto"
@@ -51,6 +52,14 @@ func init() {
 	ctx = storage.GetContext()
 }
 
+// OnPayment is a callback for NEP-17 compatible native GAS and NEO contracts.
+func OnPayment(from interop.Hash160, amount int, data interface{}) {
+	caller := runtime.GetCallingScriptHash()
+	if !bytesEqual(caller, []byte(gasHash)) && !bytesEqual(caller, []byte(neoHash)) {
+		panic("onPayment: alphabet contract accepts GAS and NEO only")
+	}
+}
+
 func Init(addrNetmap []byte) {
 	if storage.Get(ctx, netmapContractKey) != nil {
 		panic("contract already deployed")
diff --git a/alphabet/az/az_contract.go b/alphabet/az/az_contract.go
index b01f365..8a73d42 100644
--- a/alphabet/az/az_contract.go
+++ b/alphabet/az/az_contract.go
@@ -1,6 +1,7 @@
 package alphabetcontract
 
 import (
+	"github.com/nspcc-dev/neo-go/pkg/interop"
 	"github.com/nspcc-dev/neo-go/pkg/interop/binary"
 	"github.com/nspcc-dev/neo-go/pkg/interop/contract"
 	"github.com/nspcc-dev/neo-go/pkg/interop/crypto"
@@ -33,7 +34,7 @@ const (
 
 	netmapContractKey = "netmapScriptHash"
 
-	threshold = totalAlphabetContracts * 2 / 3 + 1
+	threshold = totalAlphabetContracts*2/3 + 1
 	voteKey   = "ballots"
 
 	totalAlphabetContracts = 7
@@ -51,6 +52,14 @@ func init() {
 	ctx = storage.GetContext()
 }
 
+// OnPayment is a callback for NEP-17 compatible native GAS and NEO contracts.
+func OnPayment(from interop.Hash160, amount int, data interface{}) {
+	caller := runtime.GetCallingScriptHash()
+	if !bytesEqual(caller, []byte(gasHash)) && !bytesEqual(caller, []byte(neoHash)) {
+		panic("onPayment: alphabet contract accepts GAS and NEO only")
+	}
+}
+
 func Init(addrNetmap []byte) {
 	if storage.Get(ctx, netmapContractKey) != nil {
 		panic("contract already deployed")
@@ -264,7 +273,7 @@ func bytesEqual(a []byte, b []byte) bool {
 
 func voteID(epoch interface{}, args [][]byte) []byte {
 	var (
-		result []byte
+		result     []byte
 		epochBytes = epoch.([]byte)
 	)
 
diff --git a/alphabet/buky/buky_contract.go b/alphabet/buky/buky_contract.go
index 6c289f4..5f648ac 100644
--- a/alphabet/buky/buky_contract.go
+++ b/alphabet/buky/buky_contract.go
@@ -1,6 +1,7 @@
 package alphabetcontract
 
 import (
+	"github.com/nspcc-dev/neo-go/pkg/interop"
 	"github.com/nspcc-dev/neo-go/pkg/interop/binary"
 	"github.com/nspcc-dev/neo-go/pkg/interop/contract"
 	"github.com/nspcc-dev/neo-go/pkg/interop/crypto"
@@ -33,7 +34,7 @@ const (
 
 	netmapContractKey = "netmapScriptHash"
 
-	threshold = totalAlphabetContracts * 2 / 3 + 1
+	threshold = totalAlphabetContracts*2/3 + 1
 	voteKey   = "ballots"
 
 	totalAlphabetContracts = 7
@@ -51,6 +52,14 @@ func init() {
 	ctx = storage.GetContext()
 }
 
+// OnPayment is a callback for NEP-17 compatible native GAS and NEO contracts.
+func OnPayment(from interop.Hash160, amount int, data interface{}) {
+	caller := runtime.GetCallingScriptHash()
+	if !bytesEqual(caller, []byte(gasHash)) && !bytesEqual(caller, []byte(neoHash)) {
+		panic("onPayment: alphabet contract accepts GAS and NEO only")
+	}
+}
+
 func Init(addrNetmap []byte) {
 	if storage.Get(ctx, netmapContractKey) != nil {
 		panic("contract already deployed")
@@ -264,7 +273,7 @@ func bytesEqual(a []byte, b []byte) bool {
 
 func voteID(epoch interface{}, args [][]byte) []byte {
 	var (
-		result []byte
+		result     []byte
 		epochBytes = epoch.([]byte)
 	)
 
diff --git a/alphabet/dobro/dobro_contract.go b/alphabet/dobro/dobro_contract.go
index b0e2957..33ac6b4 100644
--- a/alphabet/dobro/dobro_contract.go
+++ b/alphabet/dobro/dobro_contract.go
@@ -1,6 +1,7 @@
 package alphabetcontract
 
 import (
+	"github.com/nspcc-dev/neo-go/pkg/interop"
 	"github.com/nspcc-dev/neo-go/pkg/interop/binary"
 	"github.com/nspcc-dev/neo-go/pkg/interop/contract"
 	"github.com/nspcc-dev/neo-go/pkg/interop/crypto"
@@ -33,7 +34,7 @@ const (
 
 	netmapContractKey = "netmapScriptHash"
 
-	threshold = totalAlphabetContracts * 2 / 3 + 1
+	threshold = totalAlphabetContracts*2/3 + 1
 	voteKey   = "ballots"
 
 	totalAlphabetContracts = 7
@@ -51,6 +52,14 @@ func init() {
 	ctx = storage.GetContext()
 }
 
+// OnPayment is a callback for NEP-17 compatible native GAS and NEO contracts.
+func OnPayment(from interop.Hash160, amount int, data interface{}) {
+	caller := runtime.GetCallingScriptHash()
+	if !bytesEqual(caller, []byte(gasHash)) && !bytesEqual(caller, []byte(neoHash)) {
+		panic("onPayment: alphabet contract accepts GAS and NEO only")
+	}
+}
+
 func Init(addrNetmap []byte) {
 	if storage.Get(ctx, netmapContractKey) != nil {
 		panic("contract already deployed")
@@ -264,7 +273,7 @@ func bytesEqual(a []byte, b []byte) bool {
 
 func voteID(epoch interface{}, args [][]byte) []byte {
 	var (
-		result []byte
+		result     []byte
 		epochBytes = epoch.([]byte)
 	)
 
diff --git a/alphabet/glagoli/glagoli_contract.go b/alphabet/glagoli/glagoli_contract.go
index cb4cb7a..5c92f7f 100644
--- a/alphabet/glagoli/glagoli_contract.go
+++ b/alphabet/glagoli/glagoli_contract.go
@@ -1,6 +1,7 @@
 package alphabetcontract
 
 import (
+	"github.com/nspcc-dev/neo-go/pkg/interop"
 	"github.com/nspcc-dev/neo-go/pkg/interop/binary"
 	"github.com/nspcc-dev/neo-go/pkg/interop/contract"
 	"github.com/nspcc-dev/neo-go/pkg/interop/crypto"
@@ -33,7 +34,7 @@ const (
 
 	netmapContractKey = "netmapScriptHash"
 
-	threshold = totalAlphabetContracts * 2 / 3 + 1
+	threshold = totalAlphabetContracts*2/3 + 1
 	voteKey   = "ballots"
 
 	totalAlphabetContracts = 7
@@ -51,6 +52,14 @@ func init() {
 	ctx = storage.GetContext()
 }
 
+// OnPayment is a callback for NEP-17 compatible native GAS and NEO contracts.
+func OnPayment(from interop.Hash160, amount int, data interface{}) {
+	caller := runtime.GetCallingScriptHash()
+	if !bytesEqual(caller, []byte(gasHash)) && !bytesEqual(caller, []byte(neoHash)) {
+		panic("onPayment: alphabet contract accepts GAS and NEO only")
+	}
+}
+
 func Init(addrNetmap []byte) {
 	if storage.Get(ctx, netmapContractKey) != nil {
 		panic("contract already deployed")
@@ -264,7 +273,7 @@ func bytesEqual(a []byte, b []byte) bool {
 
 func voteID(epoch interface{}, args [][]byte) []byte {
 	var (
-		result []byte
+		result     []byte
 		epochBytes = epoch.([]byte)
 	)
 
diff --git a/alphabet/jest/jest_contract.go b/alphabet/jest/jest_contract.go
index 152dc00..d96a7e1 100644
--- a/alphabet/jest/jest_contract.go
+++ b/alphabet/jest/jest_contract.go
@@ -1,6 +1,7 @@
 package alphabetcontract
 
 import (
+	"github.com/nspcc-dev/neo-go/pkg/interop"
 	"github.com/nspcc-dev/neo-go/pkg/interop/binary"
 	"github.com/nspcc-dev/neo-go/pkg/interop/contract"
 	"github.com/nspcc-dev/neo-go/pkg/interop/crypto"
@@ -33,7 +34,7 @@ const (
 
 	netmapContractKey = "netmapScriptHash"
 
-	threshold = totalAlphabetContracts * 2 / 3 + 1
+	threshold = totalAlphabetContracts*2/3 + 1
 	voteKey   = "ballots"
 
 	totalAlphabetContracts = 7
@@ -51,6 +52,14 @@ func init() {
 	ctx = storage.GetContext()
 }
 
+// OnPayment is a callback for NEP-17 compatible native GAS and NEO contracts.
+func OnPayment(from interop.Hash160, amount int, data interface{}) {
+	caller := runtime.GetCallingScriptHash()
+	if !bytesEqual(caller, []byte(gasHash)) && !bytesEqual(caller, []byte(neoHash)) {
+		panic("onPayment: alphabet contract accepts GAS and NEO only")
+	}
+}
+
 func Init(addrNetmap []byte) {
 	if storage.Get(ctx, netmapContractKey) != nil {
 		panic("contract already deployed")
@@ -264,7 +273,7 @@ func bytesEqual(a []byte, b []byte) bool {
 
 func voteID(epoch interface{}, args [][]byte) []byte {
 	var (
-		result []byte
+		result     []byte
 		epochBytes = epoch.([]byte)
 	)
 
diff --git a/alphabet/vedi/vedi_contract.go b/alphabet/vedi/vedi_contract.go
index a5f623b..e480d08 100644
--- a/alphabet/vedi/vedi_contract.go
+++ b/alphabet/vedi/vedi_contract.go
@@ -1,6 +1,7 @@
 package alphabetcontract
 
 import (
+	"github.com/nspcc-dev/neo-go/pkg/interop"
 	"github.com/nspcc-dev/neo-go/pkg/interop/binary"
 	"github.com/nspcc-dev/neo-go/pkg/interop/contract"
 	"github.com/nspcc-dev/neo-go/pkg/interop/crypto"
@@ -33,7 +34,7 @@ const (
 
 	netmapContractKey = "netmapScriptHash"
 
-	threshold = totalAlphabetContracts * 2 / 3 + 1
+	threshold = totalAlphabetContracts*2/3 + 1
 	voteKey   = "ballots"
 
 	totalAlphabetContracts = 7
@@ -51,6 +52,14 @@ func init() {
 	ctx = storage.GetContext()
 }
 
+// OnPayment is a callback for NEP-17 compatible native GAS and NEO contracts.
+func OnPayment(from interop.Hash160, amount int, data interface{}) {
+	caller := runtime.GetCallingScriptHash()
+	if !bytesEqual(caller, []byte(gasHash)) && !bytesEqual(caller, []byte(neoHash)) {
+		panic("onPayment: alphabet contract accepts GAS and NEO only")
+	}
+}
+
 func Init(addrNetmap []byte) {
 	if storage.Get(ctx, netmapContractKey) != nil {
 		panic("contract already deployed")
@@ -264,7 +273,7 @@ func bytesEqual(a []byte, b []byte) bool {
 
 func voteID(epoch interface{}, args [][]byte) []byte {
 	var (
-		result []byte
+		result     []byte
 		epochBytes = epoch.([]byte)
 	)
 
diff --git a/alphabet/zhivete/zhivete_contract.go b/alphabet/zhivete/zhivete_contract.go
index 2a76f6f..5c060cd 100644
--- a/alphabet/zhivete/zhivete_contract.go
+++ b/alphabet/zhivete/zhivete_contract.go
@@ -1,6 +1,7 @@
 package alphabetcontract
 
 import (
+	"github.com/nspcc-dev/neo-go/pkg/interop"
 	"github.com/nspcc-dev/neo-go/pkg/interop/binary"
 	"github.com/nspcc-dev/neo-go/pkg/interop/contract"
 	"github.com/nspcc-dev/neo-go/pkg/interop/crypto"
@@ -33,7 +34,7 @@ const (
 
 	netmapContractKey = "netmapScriptHash"
 
-	threshold = totalAlphabetContracts * 2 / 3 + 1
+	threshold = totalAlphabetContracts*2/3 + 1
 	voteKey   = "ballots"
 
 	totalAlphabetContracts = 7
@@ -51,6 +52,14 @@ func init() {
 	ctx = storage.GetContext()
 }
 
+// OnPayment is a callback for NEP-17 compatible native GAS and NEO contracts.
+func OnPayment(from interop.Hash160, amount int, data interface{}) {
+	caller := runtime.GetCallingScriptHash()
+	if !bytesEqual(caller, []byte(gasHash)) && !bytesEqual(caller, []byte(neoHash)) {
+		panic("onPayment: alphabet contract accepts GAS and NEO only")
+	}
+}
+
 func Init(addrNetmap []byte) {
 	if storage.Get(ctx, netmapContractKey) != nil {
 		panic("contract already deployed")
@@ -264,7 +273,7 @@ func bytesEqual(a []byte, b []byte) bool {
 
 func voteID(epoch interface{}, args [][]byte) []byte {
 	var (
-		result []byte
+		result     []byte
 		epochBytes = epoch.([]byte)
 	)