How can I solve "expected axis -1 of input shape to have value 1 but received input with shape [None, 256, 256, 3]'" error?

I am trying to use a keras model. I trained model and want to use it from webcam. However, as far as I understand, the inputs I use while training the model and the inputs I receive from the camera do not match. How do I fix this problem?

Here code for train:

from keras.preprocessing.image import ImageDataGenerator
from keras.layers import Conv2D
from keras.layers import MaxPooling2D
from keras.layers import Dropout
from keras.layers import Dense
from keras.layers import Flatten

from keras.callbacks import EarlyStopping, ModelCheckpoint
from keras.models import Sequential, load_model
import tensorflow as tf
import numpy as np
import os

# plot pretty figures
import matplotlib
import matplotlib.pyplot as plt

plt.rcParams['axes.labelsize'] = 14
plt.rcParams['xtick.labelsize'] = 12
plt.rcParams['ytick.labelsize'] = 12

nbatch=32

train_datagen = ImageDataGenerator ( rescale=1./255,
                                     rotation_range=12.,
                                     width_shift_range=0.2,
                                     height_shift_range=0.2,
                                     zoom_range=0.15,
                                     horizontal_flip=True)

test_datagen = ImageDataGenerator (rescale=1./255)

train_gen = train_datagen.flow_from_directory(
    'images/train/',
    target_size=(256,256),
    color_mode='grayscale',
    batch_size=nbatch,
    classes=['NONE','ONE','TWO','THREE','FOUR','FIVE'],
    class_mode='categorical'
)

test_gen = test_datagen.flow_from_directory(
    'images/test/',
    target_size=(256,256),
    color_mode='grayscale',
    batch_size=nbatch,
    classes=['NONE','ONE','TWO','THREE','FOUR','FIVE'],
    class_mode='categorical'
)

for X, y in train_gen:
    print(X.shape, y.shape)

    plt.figure(figsize=(16,16))
    for i in range(25):
        plt.subplot(5,5,i+1)
        plt.axis('off')
        plt.title('Label: {}'.format(np.argmax(y[i])))
        img= np.uint8(255*X[i,:,:,0])
        plt.imshow(img,cmap='gray')
    break

plt.show()

model = Sequential()
model.add(Conv2D(32,(3,3),activation='relu',input_shape=(256,256,1)))
model.add(MaxPooling2D((2,2)))
model.add(Conv2D(64,(3,3),activation='relu'))
model.add(Conv2D(64,(3,3),activation='relu'))
model.add(MaxPooling2D((2,2)))
model.add(Conv2D(128,(3,3),activation='relu'))
model.add(MaxPooling2D((2,2)))
model.add(Conv2D(256,(3,3),activation='relu'))
model.add(MaxPooling2D((2,2)))
model.add(Flatten())
model.add(Dense(150, activation='relu'))
model.add(Dropout(0.25))
model.add(Dense(6,activation='softmax'))

model.summary()

model.compile(optimizer='adam',loss='categorical_crossentropy',metrics=['acc'])

callback_list=[EarlyStopping(monitor='val_loss',patience=10),
               ModelCheckpoint(filepath='model_6cat_2.h6',monitor='val_loss',save_best_only=True),]

os.environ["CUDA_VISIBLE_DEVİCES"] = "0"
with tf.device('/GPU:0'):
    history = model.fit_generator(
        train_gen,
        steps_per_epoch=64,
        epochs=200,
        validation_data=test_gen,
        validation_steps=28,
        callbacks=callback_list
    )

plt.figure(figsize=(16,6))
plt.subplot(1,2,1)
nepochs=len(history.history['loss'])
plt.plot(range(nepochs),history.history['loss'], 'g-', label='train')
plt.plot(range(nepochs),history.history['val_loss'], 'c-', label='test')
plt.legend(prop={'size':20})
plt.ylabel('loss')
plt.xlabel('number of epochs')
plt.subplot(1,2,2)
plt.plot(range(nepochs),history.history['acc'], 'g-', label='train')
plt.plot(range(nepochs),history.history['val_acc'], 'c-', label='test')
plt.legend(prop={'size':20})
plt.ylabel('accuracy')
plt.xlabel('number of epochs')


X_test, y_test= [], []
for ibatch, (X,y) in enumerate(test_gen):
    X_test.append(X)
    y_test.append(y)
    ibatch+=1
    if (ibatch==5*28):break

X_test = np.concatenate(X_test)
y_test = np.concatenate(y_test)
y_test = np.int32([np.argmax(r) for  r in y_test])


y_pred = np.int32([np.argmax(r) for  r in model.predict(X_test)])
match=(y_test == y_pred)
print(("Testing Accuracy = {}").format(np.sum(match)*100/match.shape[0]))

Here code for predict:

model = load_model("C://Users//90544//OneDrive//Masaüstü//Yusuf// 
ödevler//kerasGiris//model_6cat_2.h6", compile = True)

  cap = cv2.VideoCapture(0)
  while 1:
    ret, frame = cap.read()
    if ret:
        frame = cv2.flip(frame, 1)
        frame = cv2.cvtColor(frame, cv2.COLOR_BGR2GRAY)
        frame = cv2.resize(frame, (256, 256))
        frameNp = image.img_to_array(frame)
        frameNp = np.expand_dims(frameNp, axis=0)

        predictions = model.predict(frameNp)
        print(predictions)

        cv2.imshow("frame", frameNp)

        k = cv2.waitKey(1) & 0xff
        if k == 27: break  # ESC pressed

    cap.release()
    cv2.destroyAllWindows()

ValueError: Input 0 of layer sequential is incompatible with the layer: expected axis -1 of input shape to have value 1 but received input with shape [None, 256, 256, 3]

I tried to change the shape of the image I got from the camera, but I couldn't decide what the dimensions should be.