SQLite is a database on the disk, it is very useful for development purposes, however services like Heroku expect your server-side code to be stateless, which as a consequence does not really allow for databases such as SQLite. I guess you could make it work (provided you find a place on Heroku's disk where to put your SQLite db) but you would constantly lose your database's content every time you redeploy.
For Heroku specifically, I'll redirect you to this link which explains how to use Django with PostgreSQL on Heroku.
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