When you write (sell) an option, you must be covered or you must put up margin. For margin purposes, covered means that you:
Own the underlying stock
Own a call with same or lower strike price with the same or longer expiration
Long a security convertible into the underlying stock
Long a warrant with a lower exercise price than the call’s exercise price
Long an Escrow Receipt or Depository Receipt
Some common examples of a short call being covered would be long a Calendar, Diagonal or Vertical spread. In your example, if the call sold was at a lower strike than the call bought, it would not be covered and the margin required would be the difference in strikes less the premium received. Conversely, if the call sold was at a higher strike than the call bought, it would be covered, there would be no margin and you would only have to put up the cost of the spread. For a synthetic, this is a technicality in definition rather than a risk differential.
If Robinhood is allowing you to open this position then the assumption would be there should be no problem with it. However, assumptions can get you into trouble so you should contact Robinhood find out how they handle such situations.
If this is a bullish vertical spread and both calls are in-the-money, you should be looking to close out the position since you are approaching the maximum gain. Trying to squeeze out the last dime or so often costs a lot more if the underlying reverses. Any decent platform will offer combination orders. I don't know how bare bones the RH platform is but if they offer combo orders, use a spread order to facilitate getting the best exit price.
