diff --git a/waku/waku_rln_relay/conversion_utils.nim b/waku/waku_rln_relay/conversion_utils.nim
index 29503e28e..b8ee486f5 100644
--- a/waku/waku_rln_relay/conversion_utils.nim
+++ b/waku/waku_rln_relay/conversion_utils.nim
@@ -119,15 +119,19 @@ proc serialize*(memIndices: seq[MembershipIndex]): seq[byte] =
 proc serialize*(witness: Witness): seq[byte] =
   ## Serializes the witness into a byte array according to the RLN protocol format
   var buffer: seq[byte]
-  buffer.add(witness.identity_secret)
-  buffer.add(witness.user_message_limit.toBytesBE())
-  buffer.add(witness.message_id.toBytesBE())
+  # Convert Fr types to bytes and add them to buffer
+  buffer.add(@(witness.identity_secret))
+  buffer.add(@(witness.user_message_limit))
+  buffer.add(@(witness.message_id))
+  # Add path elements length as uint64 in little-endian
   buffer.add(toBytes(uint64(witness.path_elements.len), Endianness.littleEndian))
+  # Add each path element
   for element in witness.path_elements:
-    buffer.add(element)
+    buffer.add(@element)
+  # Add remaining fields
   buffer.add(witness.identity_path_index)
-  buffer.add(witness.x)
-  buffer.add(witness.external_nullifier)
+  buffer.add(@(witness.x))
+  buffer.add(@(witness.external_nullifier))
   return buffer
 
 proc toEpoch*(t: uint64): Epoch =
diff --git a/waku/waku_rln_relay/group_manager/on_chain/group_manager.nim b/waku/waku_rln_relay/group_manager/on_chain/group_manager.nim
index 54998dcb9..4e6312e84 100644
--- a/waku/waku_rln_relay/group_manager/on_chain/group_manager.nim
+++ b/waku/waku_rln_relay/group_manager/on_chain/group_manager.nim
@@ -248,22 +248,16 @@ method withdrawBatch*(
 ): Future[void] {.async: (raises: [Exception]).} =
   initializedGuard(g)
 
-proc convertUint256SeqToByteSeq(input: seq[UInt256]): seq[seq[byte]] =
-  result = newSeq[seq[byte]](input.len)
-  for i, uint256val in input:
-    # Convert UInt256 to a byte sequence (big endian)
-    let bytes = uint256val.toBytesBE()
-    result[i] = @bytes
+proc toArray32*(s: seq[byte]): array[32, byte] =
+  var output: array[32, byte]
+  discard output.copyFrom(s)
+  return output
 
-proc uinttoSeqByte*(value: uint64): seq[byte] =
-  ## Converts a uint64 to a sequence of bytes (big-endian)
-  result = newSeq[byte](8)
-  for i in 0 ..< 8:
-    result[7 - i] = byte((value shr (i * 8)) and 0xFF)
-
-proc toSeqByte*(value: array[32, byte]): seq[byte] =
-  ## Converts an array[32, byte] to a sequence of bytes
-  result = @value
+proc toArray32Seq*(values: seq[UInt256]): seq[array[32, byte]] =
+  ## Converts a sequence of UInt256 to a sequence of 32-byte arrays
+  result = newSeqOfCap[array[32, byte]](values.len)
+  for value in values:
+    result.add(value.toBytesLE())
 
 method generateProof*(
     g: OnchainGroupManager,
@@ -281,17 +275,16 @@ method generateProof*(
   if g.userMessageLimit.isNone():
     return err("user message limit is not set")
 
-  let pathElements = convertUint256SeqToByteSeq(g.merkleProofCache)
   let externalNullifierRes = poseidon(@[@(epoch), @(rlnIdentifier)])
 
   let witness = Witness(
-    identity_secret: g.idCredentials.get().idSecretHash,
-    user_message_limit: g.userMessageLimit.get(),
-    message_id: messageId,
-    path_elements: pathElements,
-    identity_path_index: uinttoSeqByte(g.membershipIndex.get()),
-    x: data,
-    external_nullifier: toSeqByte(externalNullifierRes.get()),
+    identity_secret: g.idCredentials.get().idSecretHash.toArray32(),
+    user_message_limit: serialize(g.userMessageLimit.get()),
+    message_id: serialize(messageId),
+    path_elements: toArray32Seq(g.merkleProofCache),
+    identity_path_index: @(toBytes(g.membershipIndex.get(), littleEndian)),
+    x: toArray32(data),
+    external_nullifier: externalNullifierRes.get(),
   )
 
   let serializedWitness = serialize(witness)
diff --git a/waku/waku_rln_relay/protocol_types.nim b/waku/waku_rln_relay/protocol_types.nim
index 9e43e7800..e0019990b 100644
--- a/waku/waku_rln_relay/protocol_types.nim
+++ b/waku/waku_rln_relay/protocol_types.nim
@@ -52,14 +52,17 @@ type RateLimitProof* = object
   ## the external nullifier used for the generation of the `proof` (derived from poseidon([epoch, rln_identifier]))
   externalNullifier*: ExternalNullifier
 
-type Witness* = object ## Represents the custom witness for generating an RLN proof
-  identity_secret*: seq[byte] # Identity secret (private key)
-  user_message_limit*: UserMessageLimit # Maximum number of messages a user can send
-  message_id*: MessageId # Message ID (used for rate limiting)
-  path_elements*: seq[seq[byte]] # Merkle proof path elements
-  identity_path_index*: seq[byte] # Merkle proof path indices
-  x*: seq[byte] # Hash of the signal data
-  external_nullifier*: seq[byte] # Hash of epoch and RLN identifier
+type
+  Fr = array[32, byte] # Field element representation (256 bits)
+
+  Witness* = object
+    identity_secret*: Fr
+    user_message_limit*: Fr
+    message_id*: Fr
+    path_elements*: seq[Fr]
+    identity_path_index*: seq[byte]
+    x*: Fr
+    external_nullifier*: Fr
 
 type ProofMetadata* = object
   nullifier*: Nullifier