Thank you for reaching out to the Community! I can definitely understand how helpful it would be to insert a slideshow into your campaigns. At this time being able to add a slideshow is not a feature that is currently available. This is a feature request I have submitted in your account to the appropriate teams. In the meantime I would suggest creating a slideshow in a different program then connecting it through a URL link in your text or a button. Another workaround you can try is creating your slideshow as a gif instead.
Frankie P. Community & Social Media Support
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