if you are going HTTPS on your side you need to ensure that your Marketo LP's are also HTTPS - It's a fairly straightforward process to get Marketo to setup SSL - just supply the cert and follow the instructions in the doc attached. Once installed and ready to go you will need to: Re-approve all landing pages, which you can do in bulk by going to Design Studio, then clicking on “Landing Pages”. You can now multi-select pages and unapproved and approve again via the “Landing Page Actions” menu. It is also recommended to change all images, JavaScript files and other external links in landing pages to HTTPS, otherwise users may get an “Insecure Content on Secure Pages” error. Also update any images that are hard-coded into the template. If you include a Marketo landing page on a secure website using an iframe, you will need to load the secure version of the landing page, otherwise the end user will get a security warning. If you use a Marketo Form on a Non-Marketo Page, you will need to update the Post URL to HTTPS. If you do a server-side post to a Marketo Form and you use your CNAME as the Post URL, you also need to change that to HTTPS
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