I can’t connect to my friends world even though we are both online and signed into xbox live

Even though both of us are online and signed in it wont let us connect, we don't even see each other. Some days it will work for multiple uses but other days not once. Please solve this problem because this is really annoying. A different way to connect to friends without xbox could help too.

 

Thank you for taking your time to look at this.

 

DerpyGamerBro

 

p.s my friend plays on a ps4 and myself on an IOS.