Kindly check ,
i followed to your last answer that we need to pass the authmode while connecting,
i have don that too , but still no luck

i am trying on ESP32 and SIM900A

class InitSimData():
def init(self):
self.gsm = machine.UART(1,tx=2, rx=4, timeout=1000, baudrate=9600)
time.sleep(interval)
self.check_sim()

    time.sleep(interval)
    self.register_sim()

    # time.sleep(interval)
    # self.getOPR()

    time.sleep(interval)
    self.attachGPRS()

    time.sleep(interval)
    self.rquestIPwithAPN()

    time.sleep(interval)
    self.getCGDCONT()

    # time.sleep(interval)
    # self.qosProfile()

    # time.sleep(interval)
    # self.qosProfilenext()


    time.sleep(interval)
    self.checkIP()

    time.sleep(interval)
    self.PDPcontext()


    time.sleep(interval)
    self.attachGSMtoPPP()


    

    
    
    

    
    

    


def check_sim(self):
    while True:
        self.gsm.write("AT\r\n")
        status = self.read_status()
        if status == "OK":
            print("Sim Initialized with status with status",status)
            return True
        else:
            pass
def register_sim(self):
    while True:
        self.gsm.write("AT+CREG?\r\n")
        status = self.read_status()
        if status == "+CREG: 0,1":
            print("Sim Registered with status with status",status)
            return True
        else:
            pass
def getOPR(self):
    while True:
        self.gsm.write("AT+COPS?\r\n")
        status = self.read_first()
        if status.startswith('+COPS'):
            print("Sim Operator Name is",status)
            return True
        else:
            pass

def attachGPRS(self):
    while True:
        self.gsm.write("AT+CGATT?\r\n")
        status = self.read_first()
        print("GPRS Status")
        if status == "+CGATT: 1":
            print("GPRS Attached with status with status", status)
            return True
        else:
            pass
def rquestIPwithAPN(self):
    self.gsm.write('AT+CGDCONT=1,"IP","portalnmms",\r\n')
    status = self.read_status()
    print("Checking status for CDGCONT response--",status)
    if status == 'OK':
        print("Sim Connected with APN and IP Address is ", status)
        return status
    else:
        self.rquestIPwithAPN()

def getCGDCONT(self):
    self.gsm.write('AT+CGDCONT=?\r\n')
    status = self.read_first()
    print("IP Details--",status)
    if status.startswith('+CGDCONT'):
        print("Sim Connected with IP---- ", status)
        return status
    else:
        time.sleep(1)
        self.getCGDCONT()

def getCGDCONTsec(self):
    self.gsm.write('AT+CGDCONT=?\r\n')
    status = self.read_status()
    print("IP Sec st Details--",status)
    if not status == '':
        print("Sim sec st Connected with IP---- ", status)
        return status
    else:
        time.sleep(1)
        self.getCGDCONT()

def qosProfile(self):
    """Define a QoS profile for PDP context 1, with
    Traffic Class 3 (background), maximum bit rate
    64 kb/s both for UL and for DL, no Delivery Order
    requirements, a maximum SDU size of 320
    octets, an SDU error ratio of 10-4
    , a residual bit
    error ratio of 10-5
    , delivery of erroneous SDUs
    allowed and Traffic Handling Priority 3."""

    self.gsm.write('AT+CGEQREQ=1,3,64,64,,,0,320,"1E4","1E5",1,,3\r\n')
    status = self.read_first()
    print("Qos Profile",status)
    if not status== '':
        print("Sim QOS Status---- ", status)
        return status
    else:
        time.sleep(1)
        self.qosProfile()

def PDPcontext(self):
    """PDP context 1 activation (alternatively with
        AT+CGDATA="PPP", 1 or ATD*99***1#)."""

    self.gsm.write('AT+CGDATA="PPP",1\r\n')
    status = self.read_first()
    print("CGDDATA PP ATTACHED ----", status)
    if status.startswith('CONNECT'):
        print("CGDDATA context 1 activation---- ", status)
        return status
    else:
        time.sleep(1)
        self.PDPcontext()

def checkIP(self):
    """Show address of PDP context 1. If PPP is used
        this command shall be sent from another AT
        command interface."""

    self.gsm.write('AT+CGPADDR=1\r\n')
    status = self.read_first()
    print("checkip method --",status)
    if status.startswith('+CGPADDR'):
        print("PDP context 1 activation---- ", status)
        return status
    else:
        time.sleep(1)
        self.checkIP()



def attachGSMtoPPP(self):
    import network
    GPRS=network.PPP(self.gsm)
    GPRS.active(True)
    GPRS.connect(authmode=GPRS.AUTH_PAP, username="", password="")
    if GPRS.isconnected():
        print(GPRS.ifconfig())
        return True
    else:
        time.sleep(0.5)
        self.attachGSMtoPPP()




        

        

def read_status(self):
    self.gsm.readline()
    status = self.gsm.readline()
    if status:
        status = status.decode().replace('\r\n','')
        return status
    else:
        print("Sim Module Not Connected or UART using by other device")
def read_first(self):
    status = self.gsm.readline()
    if status:
        status = status.decode().replace('\r\n','')
        return status
    else:
        print("Sim Module Not Connected or UART using by other device")

if name == "main":

print("Calling Main File")
time.sleep(10)
print("Starting the Sim Initailization Process")
sim = InitSimData()

-------------------------###########################------------ output logs are ----

gsm = machine.UART(1, rx=4, tx=2, baudrate=9600,timeout=1000)
gsm.write('AT\r\n')
4
print(gsm.readline())
b'\r\n'
print(gsm.readline())
b'OK\r\n'
print(gsm.read())
None
gsm.write('AT\r\n')
4
print(gsm.read())
b'\r\nOK\r\n'
gsm.write('AT+CGDCONT=1,"IP","portalnmms"\r\n')
32
print(gsm.read())
b'\r\nOK\r\n'
gsm.write('AT+CGDATA="PPP",1\r\n')
19
print(gsm.read())
b'\r\nERROR\r\n'

gsm.write('ATD99**1#\r\n')
13
print(gsm.read())
b'\r\n\r\nCONNECT\r\n\r\n'

GPRS=network.PPP(gsm)

GPRS.active(True)
True
GPRS.connect(authmode=GPRS.AUTH_PAP, username="", password="")
GPRS.isconnected()
False
GPRS.isconnected()
False
GPRS.isconnected()
False
GPRS.isconnected()