Need to prevent GAS web app instances from colliding

[AnTi English]

I'm using Google Apps Script to create a web app for my Telegram bot. The web app is invoked by the bot via web hook.

My bot has an inline keyboard that you can see in action in GIF 1 below. Tapping the keyboard buttons you enter a code that appears on the screen.

My problem is when I tap the buttons a little faster, callback queries to the web app collide, which results in messed up entry. See GIF 2.

I've been racking my brain trying to figure out a way to prevent instances of the web app from collision, but I've had no luck so far.

I'm posting my code below. Please, help.

The way I see it is that every instance of the script needs more time to complete before the next one kicks in. I've tried using async/await and lockService to the best of my understanding. I've been advised to try and queue the queries, but sadly haven't been able to make it work.

function doPost(e){ 

var contents = JSON.parse(e.postData.contents); 
var query_id = contents.callback_query.id; 
var mes_id = contents.callback_query.message.message_id; 
var userinput = contents.callback_query.data; 
var message_now = contents.callback_query.message.text; 
var inline_keyboard = contents.callback_query.message.reply_markup; 
var message_upd = message_now + " " + userinput; 

var keydata = { 
method: "post", 
payload: { 
method: "editMessageText", 
chat_id: String(chat_id), 
message_id: mes_id, 
text: message_upd , 
parse_mode: "HTML", 
reply_markup: JSON.stringify(inline_keyboard) 
} 
} 

UrlFetchApp.fetch('https://api.telegram.org/bot' + token + '/', keydata); 
UrlFetchApp.fetch(url + "/answerCallbackQuery?callback_query_id=" + query_id); 
}