I'm looking to fly IXU-CMB. Since there is no non-stop, the route option I prefer is IXU-BOM-CMB on Indigo with an overnight layover in BOM. I thought that after the IXU-BOM segment (upon arrival in BOM) I would be able to exit the airport, stay at a nearby hotel, and then return to BOM airport the next morning for the BOM-CMB segment. However, on Indigo's site in the flight details, it shows "Note: De-boarding may not be allowed". What does this mean?

Do I need to buy IXU-BOM separately from BOM-CMB? It works out more expensive that way.