Quectel MC60 module with fixed wiring

Hi,
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
MC60--POWERKEY -- A15

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.