Chris Brown's Baby Mama -- Money's Not the Issue ... He's Pissed Royalty's with His Mom

Chris Brown had a $10k agreement in place with his baby mama, Nia Guzman … but when she shipped little Royalty off to hang with Chris' mom, he cut her off.

Sources close to Nia tell TMZ ... Royalty's parents finally came to an agreement on child support ... settling on $10k per month from CB, starting July 1. As we reported, Chris' camp said Nia initially wanted $15k, but he only wanted to pay $2,500.

We’re told the new deal blew up though, when Daddy wanted Royalty this week -- but she was already hanging with grandma in Virginia. Since relations between Chris and his mom have been bad for years now ... our sources say Chris got pissed.

We're told Nia's claiming this is the first time she's ever denied Chris visitation, but looks like once was enough. We broke the story ... Chris is filing to establish paternity in court, so a judge can settle their child support and custody issues.