When checking value of smsvalid you use assignment operator = instead of comparison operator ==

            else if (serialdata[pointingfinger] == '$') {
                if (smsvalid == 1) {  
                    searchcharpos = pointingfinger;
                    searchchartype = 2;
                    futstat0 = 2;
                }
                if (smsvalid == 0) {
                    stat0 = futstat0;
                    pointingfinger = 0;
                }
            }

Those AT state machines aren't easy to finetune on Arduino. I spent a lot of time debugging similar code and found out that the best way is to unit test all possible situations in visual studio or xcode. Arduino is just C++ and if you copy/paste some portions of your code to C++ IDE, after implementing few functions or classes it should work. For example, to make your code working in XCode, I had to implement some dummy Serial1 class and simplify the loop code:

class _Serial1
{
    std::string buffer{"OK\r\n"};
public:
    int available()
    {
        return (int)buffer.size();
    }
    
    char read()
    {
        char c = buffer[0];
        buffer.erase(0, 1);
        return c;
    }
} Serial1;

void loop() {
    if (enabled == 1) {
        if (stat0 == 0) {
            if (Serial1.available () > 0) {
                pointingfinger++;
                serialdata[pointingfinger] = Serial1.read();
                if (serialdata[pointingfinger] == '+') {
                    
                    searchcharpos = pointingfinger;
                    searchchartype = 1;
                    futstat0 = 1;
                }
                else if (serialdata[pointingfinger] == '$') {
                    if (smsvalid == 1) {  // ==
                        searchcharpos = pointingfinger;
                        searchchartype = 2;
                        futstat0 = 2;
                    }
                    if (smsvalid == 0) { // ==
                        stat0 = futstat0;
                        pointingfinger = 0;
                    }
                }
                else if (serialdata[pointingfinger] == '\n') {
                    stat0 = futstat0;
                    pointingfinger = 0;
                    enabled = 0;
                }
                else if (serialdata[pointingfinger] == '\r') {
                    stat0 = futstat0;
                    pointingfinger = 0;
                    enabled = 0;
                }
                else {
                    stat0 = 0;
                    pointingfinger = 0;
                }
            }
            
            if (pointingfinger == 255) {
                pointingfinger = 0;
                enabled = 0;
            }
            
        }
    }
}

And the compiler immediatelly pointed me at the incorrect assignments and also I was able to debug the code step by step and see what is happening inside.

In my situation I was interfacing SIMCOM900 gprs module and I made a state machine that allows me to write code like this:

virtual void Program()
{
    switch (Pc())
    {
        case 0: _ASSERT(strlen(mApn)>0);
                Stream() << "AT+CSTT=\"" << mApn << "\",\"\",\"\"\r\n";
                break;
        case 1: Expect("OK\r\n");
                if (Expect("+CME ERROR")) { Error("CME Error when attaching apn"); Return(false);}
                if (Timeout(25000)) Return(false);
            break;
        case 2: Stream() << "AT+CIICR\r\n"; break;
        case 3: Expect("OK\r\n");
                if (Timeout(15000)) Next(); break;
        case 4: Stream() << "AT+CIFSR\r\n"; break;
        case 5: if (ReadIpAddress()) Next();
                if (Timeout(2000)) Return(false); break; // longer?
        default: Return(true);
    }
}

Here is a bit older version of it: https://gist.github.com/gabonator/88b80d9c6b16d699d6f4234ebc3a2587