Step 1: Log in to your Tumblr account and click on the name of your blog.
Step 2: Click “Edit Theme” to open your blog's template editor. We must choose the right theme to display the ads properly.
Step 3: Click “Edit HTML” from the top. You will be taken to the HTML Code for the page.
Step 4: Choose where you want to display your ad and select “Paste” to place your ad code on your Tumblr blog.
Step 5: Click “Save + Close” to complete the changes.
For mobile: go to customize theme → advanced options → use default mobile theme (ON/OFF).
On → it will serve mobile optimized version on mobile devices (Recommended Option)
Off → it will serve desktop website on mobile devices