Problem with matching datatypes using a dynamic float* array and dynamic matrix

Basically, I'm saving some coordinates in 2 arrays, arrayX and arrayY. Then, I want to change the value of a "blank" matrix in the coordinates that are saved in the previously mentioned arrays. Will post a simpler version of the code, just so you can understand:

float* arrayX = 0;
float* arrayY = 0;
int array_size = 0;
int width = 1440;
int height = 1080;

for (i=0;i<1234;i++){
    if(flag==TRUE){
        arrayX = realloc(arrayX, ++array_size * sizeof(*arrayX));
        arrayY = realloc(arrayY, array_size * sizeof(*arrayY));
        arrayX[array_size-1] = i
        arrayY[array_size-1] = 100;
    }
}

float *matrix1 = (float *)malloc(width * height * sizeof(float*));
for (i=0; i<width*height;i++){
    *(matrix+i) = 0;
}
for (i=0; i<array_size; i++){
    *(matrix1 + arrayY[i] * width + arrayX[i]) = 255;  //ERROR HERE
}

This code gives me this error:

error: invalid operands to binary + (have 'float *' and 'float')

And I'm not understanding why:

arrayY[l] is the float pointed by arrayY + l.

*(matrix1 + float * int + float) should also be a float.

I'm clearly messing up something here, and I've scrolled to a fair share of other posts (on how to allocate the matrix, and with this error) and don't understand it/don't find exactly what I'm looking for.

I'm sure it's a pretty silly question, and with a very easy solution.

For starters the argument of the call of malloc in this declaration

float *matrix1 = (float *)malloc(width * height * sizeof(float*));
                                                  ^^^^^^^^^^^^^^

is incorrect. It seems you mean

float *matrix1 = (float *)malloc(width * height * sizeof(float));
                                                  ^^^^^^^^^^^^^

The pointer arithmetic is allowed between pointers and objects of integer types. However in this expression

*(matrix1 + arrayY[l] * width + arrayX[l]) 

you are using pointers and objects of the type float. So the compiler issues the error message.

From the C11 Standard (6.5.6 Additive operators)

2 For addition, either both operands shall have arithmetic type, or one operand shall be a pointer to a complete object type and the other shall have integer type. (Incrementing is equivalent to adding 1.)

So either use integer arrays or at least use casting as for example

*(matrix1 + ( int )( arrayY[l] * width + arrayX[l] ))