Well, it depends on the platform you're using for your story. Some allow longer songs directly, while for others, you may have to convert the song format or use third-party tools to make it compatible.
Well, 'lut gaye' is not a common phrase I'm familiar with. However, when we see 'based on true story', it usually means that there is a real - life basis behind it. Maybe 'lut gaye' is some sort of local or specific term, and without more context, it's hard to say exactly, but the 'based on true story' part gives a hint that there is some truth in the overall concept.
You can usually do it by finding the option to add media or attachments within the story creation interface and then selecting the song file from your device.
One way is to upload the song to a cloud storage service and then embed the link in each of the stories. Just make sure you have the rights to use the song. Also, check if the platform where your stories are hosted allows such embedding.
You can usually do it by finding the 'add music' option within the story creation interface of the platform you're using. It might be labeled differently depending on the app or website.