Rob Kardashian Thinks Blac Chyna Tried To Sabotage Him on Father's Day

Rob Kardashian pays Blac Chyna child support, and she flat-out lied on social media just to ruin his Father's Day ... according to sources close to Rob.

For those who missed it ... Chyna dissed both her baby daddys on her Instagram Story Sunday in a message that read: "wow Tyga and Rob ... no child support BOSS BITCH ALL 201[8]."

We're told Rob thinks it was just Chyna trying to ruin his Father's Day and egg him on to go after her ... something he's prohibited from doing, according to their custody agreement -- they made an agreement to keep all the negative stuff off social media.

For the most part, there hasn't been a lot of drama between the two recently. We're told Rob pays child support, but wants it drastically lowered because he's not making any money and the $20k a month no longer has a correlation to his ability to pay.

As for their daughter, Dream, we're told Rob never skips a visit.