Join data frames with multiple conditions

Question

I have two large data frames (gpr1 = 94991 rows and 12 vars, and eff1 = 946 rows and 21 vars). I need to join them where the VesselID matches, and where the POSITION_DATETIME from the gpr df lies inside the TripStartDateTime and the TripEndDateTime from the eff df. I am struggling to work out how to do this as I usually only join by an identifiing key and no other conditions. I have tried to add my script in all the correct ways i.e. indent all code by 4 spaces using the code toolbar button or the CTRL+K keyboard shortcut, but I can't for the life of me get it to accept my code in the question. I will include it in a comment. In summary, however, I receive the following error with the script I used: Warning: Detected an unexpected many-to-many relationship between x and y. Ultimately I end up with the error and a dataframe that has 20075981 rows and 32 vars. Any tips on adding script to stack questions would also be great! I was also unable to attach a repro data set without getting the error and stack thinking it was badly formatted script but am happy to forward this on.