Don't shows premium section / preview if unavailable.

Telegram/Resources/langs/lang.strings

@@ -1705,6 +1705,7 @@ https://github.com/telegramdesktop/tdesktop/blob/master/LEGAL
 "lng_premium_summary_agree" = "By purchasing a Premium subscription, you agree to {terms} and {policy}.";
 
 "lng_premium_success" = "You've successfully subscribed to Telegram Premium!";
+"lng_premium_unavailable" = "This feature requires subscription to **Telegram Premium**.\n\nUnfortunately, **Telegram Premium** is not available in your region.";
 
 "lng_accounts_limit_title" = "Limit Reached";
 "lng_accounts_limit1#one" = "You have reached the limit of **{count}** connected accounts.";

Telegram/SourceFiles/boxes/premium_preview_box.cpp

@@ -22,9 +22,11 @@ https://github.com/telegramdesktop/tdesktop/blob/master/LEGAL
 #include "ui/effects/path_shift_gradient.h"
 #include "ui/effects/premium_graphics.h"
 #include "ui/text/text.h"
+#include "ui/text/text_utilities.h"
 #include "ui/widgets/buttons.h"
 #include "ui/widgets/gradient_round_button.h"
 #include "ui/wrap/padding_wrap.h"
+#include "ui/boxes/confirm_box.h"
 #include "settings/settings_premium.h"
 #include "lottie/lottie_single_player.h"
 #include "history/view/media/history_view_sticker.h"
@@ -743,6 +745,10 @@ void Show(not_null<Window::SessionController*> controller, QImage back) {
 void Show(
 		not_null<Window::SessionController*> controller,
 		Descriptor &&descriptor) {
+	if (!controller->session().premiumPossible()) {
+		controller->show(Box(PremiumUnavailableBox));
+		return;
+	}
 	auto &list = Preloads();
 	for (auto i = begin(list); i != end(list);) {
 		const auto already = i->controller.get();
@@ -830,3 +836,12 @@ void ShowPremiumPreviewBox(
 		.disabled = disabled,
 	});
 }
+
+void PremiumUnavailableBox(not_null<Ui::GenericBox*> box) {
+	Ui::ConfirmBox(box, {
+		.text = tr::lng_premium_unavailable(
+			tr::now,
+			Ui::Text::RichLangValue),
+		.inform = true,
+	});
+}

Telegram/SourceFiles/boxes/premium_preview_box.h

@@ -9,6 +9,10 @@ https://github.com/telegramdesktop/tdesktop/blob/master/LEGAL
 
 class DocumentData;
 
+namespace Ui {
+class GenericBox;
+} // namespace Ui
+
 namespace Window {
 class SessionController;
 } // namespace Window
@@ -32,3 +36,5 @@ void ShowPremiumPreviewBox(
 	not_null<Window::SessionController*> controller,
 	PremiumPreview section,
 	const base::flat_map<QString, ReactionDisableType> &disabled = {});
+
+void PremiumUnavailableBox(not_null<Ui::GenericBox*> box);

Telegram/SourceFiles/settings/settings_premium.cpp

@@ -14,6 +14,7 @@ https://github.com/telegramdesktop/tdesktop/blob/master/LEGAL
 #include "info/settings/info_settings_widget.h" // SectionCustomTopBarData.
 #include "lang/lang_keys.h"
 #include "main/main_session.h"
+#include "boxes/premium_preview_box.h"
 #include "settings/settings_common.h"
 #include "settings/settings_premium.h"
 #include "ui/abstract_button.h"
@@ -23,6 +24,7 @@ https://github.com/telegramdesktop/tdesktop/blob/master/LEGAL
 #include "ui/effects/premium_graphics.h"
 #include "ui/text/text_utilities.h"
 #include "ui/text/format_values.h"
+#include "ui/layers/generic_box.h"
 #include "ui/widgets/gradient_round_button.h"
 #include "ui/widgets/labels.h"
 #include "ui/wrap/fade_wrap.h"
@@ -993,6 +995,10 @@ void ShowPremium(not_null<Main::Session*> session, const QString &ref) {
 void ShowPremium(
 		not_null<Window::SessionController*> controller,
 		const QString &ref) {
+	if (!controller->session().premiumPossible()) {
+		controller->show(Box(PremiumUnavailableBox));
+		return;
+	}
 	controller->setPremiumRef(ref);
 	controller->showSettings(Settings::PremiumId());
 }

Telegram/SourceFiles/window/section_widget.cpp

@@ -336,7 +336,7 @@ bool ShowSendPremiumError(
 		not_null<SessionController*> controller,
 		not_null<DocumentData*> document) {
 	if (!document->isPremiumSticker()
-		|| document->session().user()->isPremium()) {
+		|| document->session().premium()) {
 		return false;
 	}
 	ShowStickerPreviewBox(controller, document);