Error adding code to head

We configure tracking of conversions, their transfer to Google Analytics, through events in the tag manager, for this I try to connect it by inserting the code in the head after sending the form. Here is the code <script>(function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start': new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0], j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src= 'https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f); })(window,document,'script','dataLayer','GTM-MSPLPZH');</script> but it does not accept it and gives an error what can be done in this case?