Should we invest in lump sum or invest or invest mthly when it comes to robo investing? Which will be a more profitable approach?

For Robo, invest monthly and increase the amount when there is a dip.

Robo-advisors help in being systematic and avoid behavioral bias that pushes retail investors to buy more from excitement when the markets are growing, and sell out of fear when the markets have dropped, which is the opposite of the right strategy.

Automation minimizes or removes the room for error that can come with rebalancing and portfolio reconstruction. This automation ultimately increases the probability of higher long-term returns.

REITs is dividend play so it really depends whether you want growth or dividends play. For my strategy, I will not invest in REITs while I am still young (late 20s). I may shift a large percentage of my portfolio to REITs after 50.