Fix promo activation on /start command

src/handlers/start.rs

@@ -22,9 +22,10 @@ pub async fn start_cmd_handler(bot: Bot, msg: Message, cmd: StartCommands,
             StartCommands::Start(promo_code) if promo_code.starts_with(PROMO_START_PARAM_PREFIX) => {
                 metrics::CMD_PROMO.invoked_by_deeplink.inc();
                 let user = msg.from().expect("user must be present here");
-                let promo_code = promo_code.strip_prefix(PROMO_START_PARAM_PREFIX)
+                let encoded_promo_code = promo_code.strip_prefix(PROMO_START_PARAM_PREFIX)
                     .expect("promo start param prefix must be present here");
-                promo_activation_impl(repos.promo, user, promo_code).await?
+                let promo_code = decode_promo_code(encoded_promo_code)?;
+                promo_activation_impl(repos.promo, user, &promo_code).await?
             }
             StartCommands::Start(_) => {
                 metrics::CMD_START_COUNTER.inc();
@@ -36,3 +37,9 @@ pub async fn start_cmd_handler(bot: Bot, msg: Message, cmd: StartCommands,
     reply_html(bot, msg, answer).await?;
     Ok(())
 }
+
+fn decode_promo_code(promo_code_base64: &str) -> anyhow::Result<String> {
+    let bytes = base64::decode_engine(promo_code_base64, &base64::engine::general_purpose::URL_SAFE_NO_PAD)?;
+    let promo_code = String::from_utf8(bytes)?;
+    Ok(promo_code)
+}