Is SIM network unlocking using app normal if phone simply expects a code? I bought a rare version of Galaxy S10 which was out-of-stock in my country so the distributor got it for me from another country. But by mistake the phone is locked to original network operator in the country of origin. I was offered to send the phone back for unlocking/change but it can take a few weeks. So I decided to try online unlocking service. All looks good except of the requirement to do the unlocking via side-loaded app instead of entering the code directly. Is it normal that the 8-digit unlock code does not work directly in unlock screen but it needs a helper app?

Their e-mail after purchase of unlocking code contained instructions similar to these:


  Please make sure that your phone is on the stock factory firmware. Unlock code will work correctly only on the stock factory firmware.
  
  
  Connect your phone to Wi-Fi network and download and install  official Unlocker tool:
  https://www.htconlineunlock.net/---path-was-removed---
  Power off the phone by long pressing power button and then Power off icon.
  Remove the sim card from the phone and switch on the phone.
  Run the Unlocker tool you installed.
  Tap 'Proceed' button. Wait until your phone communicates with servers.
  The phone will ask you to enter SIM Network Unlock Pin. Enter the code, tap 'Unlock' button and wait for result.
  Message "Your device is now unlocked" appears. Long press the power button, choose 'Restart' and confirm.
  


They claim they bought the code directly from the operator. So why direct unlock does not work (I made one attempt) but I am instructed to run an app?
Such unlock apps aren't official.

They employ various methods of unlocking based on the information they gather from the app installed and querying from supposedly authentic database of unlock codes. 

I have personally used an unlock service for an iPhone which was locked to a carrier. I needed to supply device information and within a few hours they reverted with the code, which worked. All at a pittance of $10. I chatted with them and they revealed their modus operandi. Official unlock codes are obtained (read stolen) from the carrier database and these operators pay to obtain these. Payment is done only after unlocking is successful.

Bottom line is that there is nothing official or expected in such methods. If it works, good, else ask for refund