diff --git a/packages/core/js-client/src/api.ts b/packages/core/js-client/src/api.ts
index 2544b522..c22f8f19 100644
--- a/packages/core/js-client/src/api.ts
+++ b/packages/core/js-client/src/api.ts
@@ -53,10 +53,20 @@ const isAquaConfig = (
  * @param script - air script with function execution logic generated by the Aqua compiler
  */
 export const v5_callFunction = async (
-  args: (JSONValue | ServiceImpl[string])[],
+  args: [
+    client: FluencePeer | (JSONValue | ServiceImpl[string]),
+    ...args: (JSONValue | ServiceImpl[string])[],
+  ],
   def: FunctionCallDef,
   script: string,
 ): Promise<unknown> => {
+  const [peer, ...rest] = args;
+
+  if (!(peer instanceof FluencePeer)) {
+    await v5_callFunction([getDefaultPeer(), ...rest], def, script);
+    return;
+  }
+
   const argNames = Object.keys(def.arrow);
   const schemaArgCount = argNames.length;
 
@@ -65,30 +75,15 @@ export const v5_callFunction = async (
   const schemaFunctionArgs: Record<string, FunctionArg> =
     def.arrow.domain.tag === "nil" ? {} : def.arrow.domain.fields;
 
-  let peer: FluencePeer | undefined;
-
-  if (args[0] instanceof FluencePeer) {
-    peer = args[0];
-    args = args.slice(1);
-  } else {
-    peer = Fluence.defaultClient;
-  }
-
-  if (peer == null) {
-    throw new Error(
-      "Could not register Aqua service because the client is not initialized. Did you forget to call Fluence.connect()?",
-    );
-  }
-
   // if args more than expected in schema (schemaArgCount) then last arg is config
-  const config = schemaArgCount < args.length ? args.pop() : undefined;
+  const config = schemaArgCount < rest.length ? rest.pop() : undefined;
 
   if (!isAquaConfig(config)) {
     throw new Error("Config should be object type");
   }
 
   const callArgs = Object.fromEntries<JSONValue | ServiceImpl[string]>(
-    args.slice(0, schemaArgCount).map((arg, i) => {
+    rest.slice(0, schemaArgCount).map((arg, i) => {
       const argSchema = schemaFunctionArgs[argNames[i]];
 
       if (argSchema.tag === "arrow") {
@@ -133,44 +128,58 @@ export const v5_callFunction = async (
   return aqua2ts(result, returnSchema);
 };
 
+const getDefaultPeer = (): FluencePeer => {
+  if (Fluence.defaultClient == null) {
+    throw new Error(
+      "Could not register Aqua service because the client is not initialized. Did you forget to call Fluence.connect()?",
+    );
+  }
+
+  return Fluence.defaultClient;
+};
+
+const getDefaultServiceId = (def: ServiceDef) => {
+  if (def.defaultServiceId == null) {
+    throw new Error("Service ID is not provided");
+  }
+
+  return def.defaultServiceId;
+};
+
+type RegisterServiceType =
+  | [ServiceImpl]
+  | [string, ServiceImpl]
+  | [FluencePeer, ServiceImpl]
+  | [FluencePeer, string, ServiceImpl];
+
 /**
  * Convenience function to support Aqua `service` generation backend
  * The compiler only need to generate a call the function and provide the corresponding definitions and the air script
  * @param args - raw arguments passed by user to the generated function
  * @param def - service definition generated by the Aqua compiler
  */
-export const v5_registerService = (args: unknown[], def: ServiceDef): void => {
-  // eslint-disable-next-line @typescript-eslint/consistent-type-assertions
-  const serviceImpl = args.pop() as ServiceImpl;
-  let peer: FluencePeer | undefined;
-  let serviceId = def.defaultServiceId;
-
-  if (args[0] instanceof FluencePeer) {
-    peer = args[0];
-    args = args.slice(1);
-  } else {
-    peer = Fluence.defaultClient;
-  }
-
-  if (peer == null) {
-    throw new Error(
-      "Could not register Aqua service because the client is not initialized. Did you forget to call Fluence.connect()?",
+export const v5_registerService = (
+  args: RegisterServiceType,
+  def: ServiceDef,
+): void => {
+  if (args.length === 1) {
+    v5_registerService(
+      [getDefaultPeer(), getDefaultServiceId(def), args[0]],
+      def,
     );
-  }
 
-  if (args.length === 2) {
-    if (typeof args[0] !== "string") {
-      throw new Error(
-        `Service ID should be of type string. ${typeof args[0]} provided.`,
-      );
+    return;
+  } else if (args.length === 2) {
+    if (args[0] instanceof FluencePeer) {
+      v5_registerService([args[0], getDefaultServiceId(def), args[1]], def);
+      return;
+    } else {
+      v5_registerService([getDefaultPeer(), args[0], args[1]], def);
+      return;
     }
-
-    serviceId = args[0];
   }
 
-  if (serviceId == null) {
-    throw new Error("Service ID is not provided");
-  }
+  const [peer, serviceId, serviceImpl] = args;
 
   // Schema for every function in service
   const serviceSchema = def.functions.tag === "nil" ? {} : def.functions.fields;