Delivering music online is hard. Not technically hard but legally hard. The reason for that is that there are two copyrights in a recorded song: the recording itself and then the song which is contained within that recording - the actual written words and melody.
You may well know all of this already, but a lot of people don't - or haven't fully appreciated the complexity, so I apologise if I'm telling you something you already know!
Butnwhat this means is that even if you have the agreement of the person who owns the recording to be allowed to use that recording in a stream, as soon as you make that recording available to stream you need the agreement of whoever wrote the music.
The complicated bit here is this - even if the artist owns the rights to the recording AND they wrote the song they may not actually be able to assign you the rights because quite often they have assigned the representation of their rights in the songwriting copyright to an organisation like PRS/MCPS (in the U.K. for example) - who are then required to pursue for a royalty payment anyone using the songwriting element (which is contained within the recording). The reason they assign these rights is that it makes certain things around songwriting royalty collection easier. Songwriters are paid for the use of their copyright - for example if their song is played by a DJ in a club - but the payments are often small and they cannot possibly grant a license to every single DJ who wants to play their song and they also can't admin the collection of that payment.
This causes a headache for people who want to provide streams of songs - because they need to negotiate a licence and associated payment with the organisations to which songwriters have assigned this element of their copyright.
And it means that - in essence - unless you've done that deal, at some point when you get big enough, one of those organisations is going to come knocking with a back dated request for payment.