diff --git a/packages/core/aqua-to-js/src/generate/__test__/__snapshots__/generate.snap.d.ts b/packages/core/aqua-to-js/src/generate/__test__/__snapshots__/generate.snap.d.ts
index 0795649f..74fee0b1 100644
--- a/packages/core/aqua-to-js/src/generate/__test__/__snapshots__/generate.snap.d.ts
+++ b/packages/core/aqua-to-js/src/generate/__test__/__snapshots__/generate.snap.d.ts
@@ -50,19 +50,19 @@ export function registerHelloWorld(peer: IFluenceClient$$, serviceId: string, se
 // Functions
 export type ResourceTestResultType = [string | null, string[]]
 
-export type resourceTestParams = [label: string, config?: {ttl?: number}] | [peer: IFluenceClient$$, label: string, config?: {ttl?: number}];
+export type ResourceTestParams = [label: string, config?: {ttl?: number}] | [peer: IFluenceClient$$, label: string, config?: {ttl?: number}];
 
 export type ResourceTestResult = Promise<ResourceTestResultType>;
 
-export type helloTestParams = [config?: {ttl?: number}] | [peer: IFluenceClient$$, config?: {ttl?: number}];
+export type HelloTestParams = [config?: {ttl?: number}] | [peer: IFluenceClient$$, config?: {ttl?: number}];
 
 export type HelloTestResult = Promise<string>;
 
-export type demo_calculationParams = [service_id: string, config?: {ttl?: number}] | [peer: IFluenceClient$$, service_id: string, config?: {ttl?: number}];
+export type Demo_calculationParams = [service_id: string, config?: {ttl?: number}] | [peer: IFluenceClient$$, service_id: string, config?: {ttl?: number}];
 
 export type Demo_calculationResult = Promise<number>;
 
-export type marineTestParams = [wasm64: string, config?: {ttl?: number}] | [peer: IFluenceClient$$, wasm64: string, config?: {ttl?: number}];
+export type MarineTestParams = [wasm64: string, config?: {ttl?: number}] | [peer: IFluenceClient$$, wasm64: string, config?: {ttl?: number}];
 
 export type MarineTestResult = Promise<number>;
 
diff --git a/packages/core/aqua-to-js/src/generate/__test__/__snapshots__/generate.snap.ts b/packages/core/aqua-to-js/src/generate/__test__/__snapshots__/generate.snap.ts
index e680d7c8..8a5cdee4 100644
--- a/packages/core/aqua-to-js/src/generate/__test__/__snapshots__/generate.snap.ts
+++ b/packages/core/aqua-to-js/src/generate/__test__/__snapshots__/generate.snap.ts
@@ -542,7 +542,7 @@ export const resourceTest_script = `
 
 export type ResourceTestResultType = [string | null, string[]]
 
-export type resourceTestParams = [label: string, config?: {ttl?: number}] | [peer: IFluenceClient$$, label: string, config?: {ttl?: number}];
+export type ResourceTestParams = [label: string, config?: {ttl?: number}] | [peer: IFluenceClient$$, label: string, config?: {ttl?: number}];
 
 export type ResourceTestResult = Promise<ResourceTestResultType>;
 
@@ -609,7 +609,7 @@ export const helloTest_script = `
 )
 `;
 
-export type helloTestParams = [config?: {ttl?: number}] | [peer: IFluenceClient$$, config?: {ttl?: number}];
+export type HelloTestParams = [config?: {ttl?: number}] | [peer: IFluenceClient$$, config?: {ttl?: number}];
 
 export type HelloTestResult = Promise<string>;
 
@@ -679,7 +679,7 @@ export const demo_calculation_script = `
 )
 `;
 
-export type demo_calculationParams = [service_id: string, config?: {ttl?: number}] | [peer: IFluenceClient$$, service_id: string, config?: {ttl?: number}];
+export type Demo_calculationParams = [service_id: string, config?: {ttl?: number}] | [peer: IFluenceClient$$, service_id: string, config?: {ttl?: number}];
 
 export type Demo_calculationResult = Promise<number>;
 
@@ -757,7 +757,7 @@ export const marineTest_script = `
 )
 `;
 
-export type marineTestParams = [wasm64: string, config?: {ttl?: number}] | [peer: IFluenceClient$$, wasm64: string, config?: {ttl?: number}];
+export type MarineTestParams = [wasm64: string, config?: {ttl?: number}] | [peer: IFluenceClient$$, wasm64: string, config?: {ttl?: number}];
 
 export type MarineTestResult = Promise<number>;
 
diff --git a/packages/core/aqua-to-js/src/generate/interfaces.ts b/packages/core/aqua-to-js/src/generate/interfaces.ts
index 7b46d5f8..73f9910f 100644
--- a/packages/core/aqua-to-js/src/generate/interfaces.ts
+++ b/packages/core/aqua-to-js/src/generate/interfaces.ts
@@ -86,7 +86,9 @@ export class TSTypeGenerator implements TypeGenerator {
     return [
       argsDesc.join("\n"),
       resTypeDesc ?? "",
-      `export type ${funcDef.functionName}Params = ${functionOverloadArgsType};`,
+      `export type ${capitalize(
+        funcDef.functionName,
+      )}Params = ${functionOverloadArgsType};`,
       `export type ${capitalize(
         funcDef.functionName,
       )}Result = Promise<${resType}>;\n`,
diff --git a/packages/core/js-client/src/api.ts b/packages/core/js-client/src/api.ts
index dfdc0b3a..acef4450 100644
--- a/packages/core/js-client/src/api.ts
+++ b/packages/core/js-client/src/api.ts
@@ -25,6 +25,7 @@ import type {
 import { CallAquaFunctionConfig } from "./compilerSupport/callFunction.js";
 import {
   aqua2ts,
+  SchemaValidationError,
   ts2aqua,
   wrapFunction,
 } from "./compilerSupport/conversions.js";
@@ -37,10 +38,11 @@ const isAquaConfig = (
   config: JSONValue | ServiceImpl[string] | undefined,
 ): config is CallAquaFunctionConfig => {
   return (
-    typeof config === "object" &&
-    config !== null &&
-    !Array.isArray(config) &&
-    ["undefined", "number"].includes(typeof config["ttl"])
+    config === undefined ||
+    (typeof config === "object" &&
+      config !== null &&
+      !Array.isArray(config) &&
+      ["undefined", "number"].includes(typeof config["ttl"]))
   );
 };
 
@@ -60,14 +62,17 @@ export const v5_callFunction = async (
   def: FunctionCallDef,
   script: string,
 ): Promise<unknown> => {
-  const [peer, ...rest] = args;
+  const [peerOrArg, ...rest] = args;
 
-  if (!(peer instanceof FluencePeer)) {
-    await v5_callFunction([getDefaultPeer(), ...rest], def, script);
+  if (!(peerOrArg instanceof FluencePeer)) {
+    await v5_callFunction([getDefaultPeer(), peerOrArg, ...rest], def, script);
     return;
   }
 
-  const argNames = Object.keys(def.arrow);
+  const argNames = Object.keys(
+    def.arrow.domain.tag === "nil" ? [] : def.arrow.domain.fields,
+  );
+
   const schemaArgCount = argNames.length;
 
   type FunctionArg = SimpleTypes | ArrowWithoutCallbacks;
@@ -88,7 +93,12 @@ export const v5_callFunction = async (
 
       if (argSchema.tag === "arrow") {
         if (typeof arg !== "function") {
-          throw new Error("Argument and schema don't match");
+          throw new SchemaValidationError(
+            [argNames[i]],
+            argSchema,
+            "function",
+            arg,
+          );
         }
 
         const wrappedFunction = wrapFunction(arg, argSchema);
@@ -97,7 +107,12 @@ export const v5_callFunction = async (
       }
 
       if (typeof arg === "function") {
-        throw new Error("Argument and schema don't match");
+        throw new SchemaValidationError(
+          [argNames[i]],
+          argSchema,
+          "non-function value",
+          arg,
+        );
       }
 
       return [
@@ -111,7 +126,7 @@ export const v5_callFunction = async (
     def.arrow.codomain.tag === "nil" || def.arrow.codomain.items.length === 0;
 
   const params = {
-    peer,
+    peer: peerOrArg,
     args: callArgs,
     config,
   };
diff --git a/packages/core/js-client/src/compilerSupport/conversions.ts b/packages/core/js-client/src/compilerSupport/conversions.ts
index 1923703e..9cf5a7c0 100644
--- a/packages/core/js-client/src/compilerSupport/conversions.ts
+++ b/packages/core/js-client/src/compilerSupport/conversions.ts
@@ -28,12 +28,12 @@ import { ParticleContext } from "../jsServiceHost/interfaces.js";
 
 import { ServiceImpl } from "./types.js";
 
-class SchemaValidationError extends Error {
+export class SchemaValidationError extends Error {
   constructor(
     public path: string[],
-    schema: NonArrowSimpleType,
+    schema: NonArrowSimpleType | ArrowWithoutCallbacks,
     expected: string,
-    provided: JSONValue,
+    provided: JSONValue | ServiceImpl[string],
   ) {
     const given =
       provided === null