Quectel MC60 module with fixed wiring

I hope this is the proper category.

I have an Arduino Mega based development board that works with Atmel Atmega 2560 processor and contains internal Quectel MC60 GSM / GNSS module

The wire connections are:

MC60_Tx -- D15
MC60_Rx -- D14
MC_RI -- D2
MC60_DTR-- D4

I'm using HttpClient.ino which comes with TinyGSM

with SerialAT Serial3 setting.

The board can connect to network, update Network Time but can't complete the HTTP GET request.

With that board I can send SMS, make audio calls but I can’t connect to an MQTT Server or use as a HttpClient.

I think Tx and Rx and Power Pins are correctly set. Can it be the problem with the other pins?

I Couldn't find anywhere where can I set these pins.

I have also tried Arduino GSM library (GSM.h)
Bu I couldn’t find where the wire settings are.
Changed the lines in the GSM3IO.h file. But board could not Initialize with the modem.