First of all Override the following file :

• change redirect URL if login post controller gets 404 error or redirect the customer to a specific page :
  
  private function applyRedirect($url) { /* changes start*/ $baseUrl = $this->storeManager->getStore()->getBaseUrl(); if($url == $baseUrl.'customer/account/loginPost/'){ $url = $baseUrl.'customer/account/login/'; } /* changes end*/ $this->session->setBeforeAuthUrl($url); }

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  private function applyRedirect($url) {    /* changes start*/     $baseUrl = $this->storeManager->getStore()->getBaseUrl();     if($url == $baseUrl.'customer/account/loginPost/'){         $url = $baseUrl.'customer/account/login/';     }    /* changes  end*/     $this->session->setBeforeAuthUrl($url); }

  
  NOTE:  Override core file in your custom module.