How to debug internet connection error?

Question

Arduino

MTS operator. SMS are sent. Any network tests (complete with IDE) work - Modem is functoning properly
GSM module sim800l
robotdyn nano v2
Load the "TestGPRS" example (where you need to manually enter apn, login, pwd).
Here is the general log

Connecting GSM network...Connecting GSM network...OK
Enter your APN: mts
Now, enter your login: mts
Finally, enter your password: Attaching to GPRS with your APN...
ERROR
Connecting GSM network...OK
Enter your APN: mts.ru
Now, enter your login: mts
Finally, enter your password: Attaching to GPRS with your APN...
ERROR
Connecting GSM network...OK
Enter your APN: internet.mts.ru
Now, enter your login: mts
Finally, enter your password: Attaching to GPRS with your APN...
ERROR
Connecting GSM network...OK
Enter your APN: mts
Now, enter your login: mts
Finally, enter your password: Attaching to GPRS with your APN...
ERROR
Connecting GSM network...OK
Enter your APN:

How to get internet?
UPD: with a megaphone, a SIM card also gives ERROR (code = 2)
codegprsAccess.attachGPRS(apn, login, password);

Answer 1

It's possible that you're just entering the wrong information.
Search the Internet for accurate data, at worst, you can call the operator and ask for the data, insert it into the phone, accept the data sent and read it.
And if this is a Ukrainian mts, then most likely a login password is not needed. If Russian -
Ordinary SIM-card "MTS"
◦APN: internet.mts.ru
◦Username: mts
◦Password: mts

Answer 2

It turned out to execute an http request using the SoftwareSerial.h library and AT commands
With GSM.h, apparently something needs to be conjured. The first thought arose that there were some troubles with delays