diff --git a/pyfragment/client.py b/pyfragment/client.py
index 7d7963a..36b7f84 100644
--- a/pyfragment/client.py
+++ b/pyfragment/client.py
@@ -4,6 +4,7 @@ import json
 from typing import Any, cast
 
 from pyfragment.core.constants import (
+    BASE_HEADERS,
     DEFAULT_TIMEOUT,
     FRAGMENT_BASE_URL,
     MNEMONIC_WORD_COUNTS_VALID,
@@ -40,6 +41,7 @@ class FragmentClient:
         cookies: Fragment session cookies as a dict or JSON string.
         wallet_version: Wallet contract version — ``"V4R2"`` or ``"V5R1"`` (default).
         timeout: HTTP request timeout in seconds. Defaults to ``30.0``.
+        headers: Custom HTTP request headers. If omitted, :data:`BASE_HEADERS` is used.
 
     Raises:
         ConfigurationError: If ``seed``, ``api_key``, or ``wallet_version`` are missing or invalid.
@@ -104,6 +106,7 @@ class FragmentClient:
         cookies: dict[str, Any] | str,
         wallet_version: str = "V5R1",
         timeout: float = DEFAULT_TIMEOUT,
+        headers: dict[str, str] | None = None,
     ) -> None:
         self._validate_required(seed, api_key)
         parsed_cookies = self._parse_cookies(cookies)
@@ -115,6 +118,7 @@ class FragmentClient:
         self.cookies: dict[str, Any] = parsed_cookies
         self.wallet_version: WalletVersion = version
         self.timeout: float = timeout
+        self.headers: dict[str, str] = headers if headers is not None else BASE_HEADERS
         self.marketplace = MarketplaceService(self)
         self.purchases = PurchasesService(self)
         self.giveaways = GiveawaysService(self)
@@ -391,4 +395,4 @@ class FragmentClient:
                 page_url="https://fragment.com/premium/gift",
             )
         """
-        return await raw_api_call(self.cookies, self.timeout, method, data, page_url)
+        return await raw_api_call(self.cookies, self.timeout, method, data, page_url, self.headers)
diff --git a/pyfragment/core/constants/__init__.py b/pyfragment/core/constants/__init__.py
index a49d4a3..4e5be9a 100644
--- a/pyfragment/core/constants/__init__.py
+++ b/pyfragment/core/constants/__init__.py
@@ -14,6 +14,8 @@ from pyfragment.core.constants.limits import (
     STARS_PURCHASE_MIN,
     STARS_WINNERS_MAX,
     STARS_WINNERS_MIN,
+    TON_TOPUP_MAX,
+    TON_TOPUP_MIN,
     TONAPI_KEY_MIN_LENGTH,
 )
 from pyfragment.core.constants.ton import DEVICE_INFO, USDT_TON_MASTER_ADDRESS
@@ -56,5 +58,7 @@ __all__ = [
     "STARS_WINNERS_MAX",
     "STARS_WINNERS_MIN",
     "TONAPI_KEY_MIN_LENGTH",
+    "TON_TOPUP_MAX",
+    "TON_TOPUP_MIN",
     "USDT_TON_MASTER_ADDRESS",
 ]
diff --git a/pyfragment/core/constants/limits.py b/pyfragment/core/constants/limits.py
index 1b71c3e..b054c80 100644
--- a/pyfragment/core/constants/limits.py
+++ b/pyfragment/core/constants/limits.py
@@ -2,7 +2,7 @@ from __future__ import annotations
 
 # Stars: direct purchase
 STARS_PURCHASE_MIN: int = 50
-STARS_PURCHASE_MAX: int = 10_000
+STARS_PURCHASE_MAX: int = 10_000_000
 
 # Stars: giveaway per winner
 STARS_GIVEAWAY_MIN: int = 500
@@ -10,12 +10,20 @@ STARS_GIVEAWAY_MAX: int = 1_000_000
 
 # Stars giveaway winners count
 STARS_WINNERS_MIN: int = 1
-STARS_WINNERS_MAX: int = 5
+STARS_WINNERS_MAX: int = 15
 
 # Premium giveaway winners count
 PREMIUM_WINNERS_MIN: int = 1
 PREMIUM_WINNERS_MAX: int = 24_000
 
+# TON topup / Ads recharge amount
+TON_TOPUP_MIN: int = 1
+TON_TOPUP_MAX: int = 1_000_000_000
+
+# Wallet minimum balances
+MIN_TON_BALANCE: float = 0.33
+MIN_USDT_BALANCE: float = 0.75
+
 # Premium subscription durations (months)
 PREMIUM_MONTHS_VALID: frozenset[int] = frozenset({3, 6, 12})
 
@@ -24,7 +32,3 @@ MNEMONIC_WORD_COUNTS_VALID: frozenset[int] = frozenset({12, 24})
 
 # Tonapi API key minimum length
 TONAPI_KEY_MIN_LENGTH: int = 68
-
-# Wallet minimum balances
-MIN_TON_BALANCE: float = 0.33
-MIN_USDT_BALANCE: float = 0.75
diff --git a/pyfragment/domains/ads/recharge.py b/pyfragment/domains/ads/recharge.py
index b79d988..c79806a 100644
--- a/pyfragment/domains/ads/recharge.py
+++ b/pyfragment/domains/ads/recharge.py
@@ -4,7 +4,7 @@ import json
 import logging
 from typing import TYPE_CHECKING
 
-from pyfragment.core.constants import ADS_TOPUP_PAGE, DEVICE_INFO
+from pyfragment.core.constants import ADS_TOPUP_PAGE, DEVICE_INFO, TON_TOPUP_MAX, TON_TOPUP_MIN
 from pyfragment.domains.tonapi.account import get_account_info
 from pyfragment.domains.tonapi.transaction import process_transaction
 from pyfragment.exceptions import ConfigurationError, FragmentAPIError, FragmentError, UnexpectedError, VerificationError
@@ -18,7 +18,7 @@ logger = logging.getLogger(__name__)
 
 
 async def recharge_ads(client: FragmentClient, account: str, amount: int) -> AdsRechargeResult:
-    if not isinstance(amount, int) or not (1 <= amount <= 1_000_000_000):
+    if not isinstance(amount, int) or not (TON_TOPUP_MIN <= amount <= TON_TOPUP_MAX):
         raise ConfigurationError(ConfigurationError.INVALID_TON_AMOUNT)
 
     try:
diff --git a/pyfragment/domains/ads/tonup.py b/pyfragment/domains/ads/tonup.py
index df3d8c0..40d999b 100644
--- a/pyfragment/domains/ads/tonup.py
+++ b/pyfragment/domains/ads/tonup.py
@@ -4,7 +4,7 @@ import json
 import logging
 from typing import TYPE_CHECKING
 
-from pyfragment.core.constants import ADS_TOPUP_PAGE, DEVICE_INFO
+from pyfragment.core.constants import ADS_TOPUP_PAGE, DEVICE_INFO, TON_TOPUP_MAX, TON_TOPUP_MIN
 from pyfragment.domains.payments import parse_required_payment_amount
 from pyfragment.domains.tonapi.account import get_account_info
 from pyfragment.domains.tonapi.transaction import process_transaction
@@ -26,7 +26,7 @@ logger = logging.getLogger(__name__)
 
 
 async def topup_ton(client: FragmentClient, username: str, amount: int, show_sender: bool = True) -> AdsTopupResult:
-    if not isinstance(amount, int) or not (1 <= amount <= 1_000_000_000):
+    if not isinstance(amount, int) or not (TON_TOPUP_MIN <= amount <= TON_TOPUP_MAX):
         raise ConfigurationError(ConfigurationError.INVALID_TON_AMOUNT)
 
     try:
diff --git a/pyfragment/domains/base.py b/pyfragment/domains/base.py
index 6dce538..2e02aa7 100644
--- a/pyfragment/domains/base.py
+++ b/pyfragment/domains/base.py
@@ -20,14 +20,16 @@ async def raw_api_call(
     method: str,
     data: dict[str, Any] | None,
     page_url: str,
+    headers: dict[str, str] | None = None,
 ) -> dict[str, Any]:
+    base = headers if headers is not None else BASE_HEADERS
     payload = {"method": method, **(data or {})}
-    headers = {**BASE_HEADERS, "referer": page_url, "x-aj-referer": page_url}
+    call_headers = {**base, "referer": page_url, "x-aj-referer": page_url}
     logger.debug("Starting Fragment API call '%s' on %s", method, page_url)
     try:
         async with httpx.AsyncClient(cookies=cookies, timeout=timeout) as session:
-            fragment_hash = await get_fragment_hash(cookies, headers, page_url, timeout)
-            response = await fragment_request(session, fragment_hash, headers, payload)
+            fragment_hash = await get_fragment_hash(cookies, call_headers, page_url, timeout)
+            response = await fragment_request(session, fragment_hash, call_headers, payload)
             logger.debug("Completed Fragment API call '%s' with response keys: %s", method, sorted(response.keys()))
             return response
     except Exception: